To what level do phono cartridges age?

In my direct experience, it's a total crap shoot.  I have cartridges that are 40 and more years old that sound wonderful.  And I have some others with similar age that are clearly not what they used to be.  I would hesitate to name names or to say that one type ages more predictably than another (MM vs MC, for example), because I have no data to point specifically at such a conclusion.  The good news is that nearly every one of the vintage MM and MI cartridges I have purchased in the last 5-8 years works fine, with maybe one exception.  (Jury is out on that one.) I would not be afraid to purchase another vintage cartridge, if I had good faith it was in NOS or near NOS condition, in terms of actual hours of use.

The stylus can wear from use. The cantilever, pole piece, magnet, coil, body and terminals are pretty much forever. That leaves the part the cantilever passes through and pivots around, the elastomer bearing. This is the part that can wear or harden over time and at least theoretically affect the sound.

It seems pretty clear to me that the elastomer bearing is the one part most responsible for the fact that every cartridge sounds better as it warms up from playing a side or two. Everything else I can think of from car tires to basketballs does eventually over time lose its elasticity, get hard, and crack. The same would sure seem to be true and put at least some time factor on a cartridge.

In practice however I have yet to run into anyone who has actually experienced this. I have a Stanton 681EEE from 1974 that near as I can tell still sounds the same as ever. All the people I have talked to, if they have any long term stories at all they are like lewm, no problems.

Now you know one thing, whatever you think the fact is I have noticed for many years now and across several different cartridges that they do warm up and sound better after playing a side or two. So I can hear that subtle (if you want to call it that, it sure ain't subtle to me!) a change over 20 minutes. A similarly subtle change over 20 years? Not so sure about that.

Fair to say I think that a cartridge probably does have a shelf life, just in effect a shelf life longer than yours.

Thanks for the info guys!