When to replace cartridge or stylus?

I have a Benz Wood H2 cartridge that I bought used about 2 years ago which supposedly had low hours on it. It sounds just fantastic in my setup. How do you know when the stylus or entire cartridge needs to be replaced? Will it slowly just degrade over time or will it something that will be obvious. If it is a slow decay then I would imagine that it would be hard to realize its performance faultering without A/B'ing with a new one. I certainly dont count the hours I play on it as some do. Also, with a Benz, is it recommeded to replace the whole cart or just have it re-tipped. Re-tipping can save you some bucks.
I have the same cartridge and you can definetly tell when it will start going bad. They say a cartridge has about a 2 yr life span but that would depend on the tracking weight used. Not that I know anything about setting up a turntable. Benz has a great buyback program where they will give you a significant discount toward a new one. Retipping is also an option. I don't know what kind of music you listen to but I heard significant differences when acoustic music was played.
Good Luck.
Go buy back after your ears tell you it is time. Re-tip are just not cost effective and the risk is high that the the process will damage the mount. In building cartridges, the cantilever and actual stylus tip are put together before they are mounted. Try to change the tip while the cantilever is inserted in the mount undermines the unit soundness.

Oh for the days when stylus was user removalable, e. g. Shure V MR's. They will be back shortly, sourced from China.
I had an ACE. Lasted about 3 or 3 1/2 years. It stopped being able to track inner grooves and complex passages. It was pretty obvious as I am really sensitive to groove distortion. I'm sure it's not a sudden thing though. It's not like it sounds perfect on record and then, bam it goes bad. It will be gradual, but eventually it will get bad enough that you will hear it. That's just my humble experience with just that one cartridges. All others have been replaced before they went bad...within 2 or 3 years.
I listen to mostly jazz and to me the cart still sounds very good. I put about 1.9g of force on it. I will just have to keep my ears open for degradation. Thanks for the info all.