How do tell when my stylus is too much worn?

I have had my MC cartridge for about 5 years. I haven't kept a proper log but I would guess about 7-800 hrs. How can I tell BY LISTENING that it is worn enough to replace or retip? Does it get edgy or shrill or....?
I suspect that the change would be so gradual that it might be hard to tell, as the ear slowly accomodates.
Of course I should remove the cartridge and view under a microscope but un mounting and remounting is a perilous business that I would like to avoid.

I just got the CBS STR-100 test record which has some tests purported to reveal wear and excessive VTF. I haven't pulled out a worn stylus to see if it works yet, though.
It has been 18 plus months or so since this thread was last updated. Poster "rauliruega" is spot on with his comments, observations and recommendations. However, he mentions that Ortofon published data on stylus tip wear. I have never been able to find such a document and I called Ortofon asking for it. So I think he means Shure and JICO, both did similar research on stylus wear hours. Their work pointed toward 400 to 500 hours of life for advanced tip shapes.

I recently took the same journey that Poster "rmm" took. What is codified in this thread is the reason why I was so confused also about critical stylus wear and hour of play life. All of the opinions expressed here are not otherwise supported by empirical research. They should be, while current cartridge manufacturers give conflicting answers to the question on critical stylus wear.

A record of my sojourn to learn how long stylus tips last is in print. As "rmm" did, I asked questions, and searched forums, looking for an answer. When I found, as in this thread, opinions that ranged all over the map, I did a deeper dive into the subject. This dive was driven to find out if my cartridge tip was worn to the point where it could damage my records. And I have a lot of records that I do not want to damage. I did not do any original research, while I am setting up to monitor my cartridge stylus tip with photomacrography. See this link to understand what that means:

I compiled everything I learned along the way into an written piece that was published in late May (2019) on The Vinyl Press. I found a lot of material on the subject that I believe will help answer your question.

See the link to my essay or discussion or article, whatever you want to call it, here:
Also, see this thread for a number of terrific responses to this article:

I think it’s pretty easy to compare used cartridge to a new cartridge (or rarely used one), i have multiple samples of the same cartridges. First thing to do is A/B test in the headphones, i have two identical turntables with two identical tonearms to do A/B test like that. If the used cartridge does not sound as good as the new one (or very low hrs one) then it’s time to think about new stylus (or new cartridge in better condition).

Any cartridge can be checked by professionals like SoudSmith or anyone else in business for about $40.

Since i’m still searching for a perfect sound i don’t want to retip any MC, because i can use the money toward another (better MC) cartridge. The more i search the more fantastic MC cartridges can be discovered. My latest discovery is Miyabi MCA from Takeda-San.

Situation is easier with MM/MI and their original styli.

My favorite cartridges are all from the 80’s and somehow i can find them in perfect condition (NOS or low hrs of use), over the years i’ve learned that very few models have serious problems with suspension/damper, those carts are top of the line Technics and Victor X-1 (not X-1II). I’ve never had any problems with vintage cartridges from many other brands/models.

In my opinion the best way to cure your cartridge is to buy another one (instead of rettipping the same one) when it comes to MC. I’ve noticed people who promote one particular model of the cartridge never tried even 20 different cartridges, so the experience is limited. For some reason they think retip is worth it. But there are so many fantastic cartridges can be purchased for the price some vendors charge just for retip.

Using a cartridge for 500hrs and then send it for retip is nonsence
MicroRidge, Gyger, MicroLine, Replicant 100 styli can be used at least for 1500 hrs or even up to 2000 hrs. Look for Shibata, Stereohedron or LineContact at least.

A used cartridge with conical or elliptical styli must be avoided for sure because of the very short life-span of such diamonds.  

@aspens  Thank you for sharing your paper. It was a very interesting read with attention to detail and acknowledgements. 
My initial reaction is ”that reminds me why I used to buy MM". Installing a new stylus is a piece of cake, of course if they are still being produced. Through this forum, @chakster , @rauliruegas and others, I've recently purchased and have been using a Stanton 881S with D81 Stereohedron stylus. As you know those stylus are no longer being produced so I was lucky to get a low hour example. As your paper points out VTF contributes to stylus wear, amazingly enough the Stanton high compliance cartridges spec is from 0.75 grams to 1.25 grams. Mine is set to 1 gram which is much lighter than a typical modern production specification for a cartridge. Your paper points out at least 20% longer life for a lighter VTF, and it seems that the high compliance cartridges of the past were leaning towards the lighter VTF, which also result in longer stylus life. 

Stanton 881S with D81 Stereohedron stylus. As you know those stylus are no longer being produced so I was lucky to get a low hour example. As your paper points out VTF contributes to stylus wear, amazingly enough the Stanton high compliance cartridges spec is from 0.75 grams to 1.25 grams.

Great cartridge and amazing stylus profile, i love Stereohedron! 

Pickering D-3000 Stereohedron is also compatible with your Stanton 881, asctually your Stanton based on Pickering XSV-3000 model. I have a NOS factory sealed D3000 Stereohedron stylus if you need a backup. 

For both Stanton and Pickering the optmal setting of VTF with brush is:

Arm setting with brush: 2 grams +/- 1/4
Resulting tracking force: 1 gram +/- 1/4
Arm setting without brush: 1 gram +/- 1/4

Norman Pickering was a noted violinist. He invented the Pickering cartridge because he didn't like how violins sounded on other cartridges. So, he is thus far one of the cartridge designers in the USA besides Joe Grado who was also a musician. Pickering's factory manager was none other than Walter Stanton, who later went out on his own. By 1960, Mr.Stanton bought out Mr.Pickering. He later established Stanton Magnetics Inc in 1961. He was the chairman and president of both Pickering & Co and Stanton Magnetics Inc until 1998. Walter O. Stanton, the inventor of an easily replaceable phonograph stylus that was crucial to creating a consumer market for audio equipment. Stanton and Pickering carts are the same with interchangeable styli despite the very different looking plastic bits and brushes - the trick is figuring out the interchanging model numbers. Pickering XSV-3000 is equal to Stanton 881s, both comes with Nude Stereohedron diamonds on alluminum cantilevers. This is the most advanced stylus shape which is achieved by grinding four flat surface on the diamond at precise angles to each other and their intersection creates areas used to contact the groove. The advantage of the Stereohedron stylus is that because of it's long and narrow contact surfaces it tracks high frequency modulation minimizing groove wear.

Norman C. Pickering, an engineer, inventor and musician whose pursuit of audio clarity and beauty helped make phonograph records and musical instruments sound better. In 1945, Mr. Pickering, who enjoyed listening to records and was frustrated by the sound quality of recordings, developed an improved pickup — that is, the mechanism that includes the phonograph needle, or stylus, and translates the information in the groove of a record into an electrical signal that can be reproduced as sound. Originally His phono pickups were designed for use in broadcast and recording studios. 1947 the demand from high-fidelity fanatics was strong enough for what’s now called a ‘cartridge’ and Pickering & Company was formed to meet the new hobby’s demands. In 1948, Mr. Pickering was among the founders of the Audio Engineering Society, now an international organization that disseminates news and information about improvements in audio technology. By the mid 50's, the Pickering company employed more than 150 people at its Plainview, Long Island headquarters. The best models, however, were introduced only in the 70's and early 80's. Pickering XSV-3000 with nude Stereohedron stylus is one of the best, a few models with higher numbers are even better.

Pickering XSV-3000 specs:

Stylus Type: Nude Stereohedron
Contact Radii: .0028 (71u)
Scanning Radii: .0003 (8u)
Stylus Tracking Force: 1 gram (+/- 0.5)
Setting with Brush: 2 gram (+/- 0.5) resulting operation tracking force 1 gram (+/- 0.5)
Frequency Response: 10 Hz to 30 kHz +
Output: 4.7 mv /cm/sec
Channel Balance: Within 1 dB @ 1kHz
Channel Separation: 35 dB @ 1kHz
Cartridge DC Resistance: 700. ohms
Cartridge Inductance: 350 mH
Cartridge Color: Brown
Load Resistance: 47k ohms or greater
Load Capacitance: 275 pF