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.

Dear @don_c55 : Yes,but M97 came with different stylus shape and inside the shape different dimension. They came: conical, two different ellipthical and hiperellipthical too.

Anyway, microridge or replicant or VDH2 goes deeper in the grooves and this helps in the quelity of listen levels. Of course that with today stylus shape the cartridge parameters for the set up has no " margin " to error if we want top quality performance levels.

Regards and enjoy the MUSIC NOT DISTORTIONS,
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.