What is the average lifespan of a phono cartridge?

This is a great question. I began buying classic used cartridges ten years ago when a new cartridge I just bought disintegrated as I was installing it. It just fell apart, the body from the mount and the stylus assembly. I always wanted a Koetsu Pro IV, at the time they were unavailable new so I took a chance on a used one. It was perfect, so I bought another one six months later and it worked great. Since then I've bought (and sold to try others) over 20 second hand "classic" cartridges and all performed fine. Go figure. I suspect people who trade cartridges are just trying something new and thus don't put many hours on them.

I have bought in 1998 a second hand mk levinson mlc-1, it has been retiped twice by Van den Hull since that date and it works quite well. When you send it for retiping the company can have a look at the rubber suspension part and change it. I use it around 4 hours a week on a big plinthed lenco with a OL conqueror mk II and am quite satisfied.

I thought people might be interested to know that my Rondo Red has just passed the 2,000 hour mark and is showing no signs of deterioration. The cartridge was initially aligned using a Mobile Fidelity Geo-Disc.

I traded the last Rondo Red in well before the 2,000 hours, which I now slightly regret, but this time I thought I'd see just how long it would actually last. I have a new Quintet Black S ready for when this happens.

All records, new or preowned, are vacuum cleaned and transferred to anti static sleeves prior to the initial play. I use a carbon/felt brush for the discs and a carbon brush for the stylus before and after each side.

No other treatments are applied.

Hope this information is helpful.

How long a cartridge will last is a kind of vague question.  More specific reference to components in the cartridge might be necessary.

Stylus shape, stylus composition, crystal orientation, tracking force, record condition, user habits and other factors contribute to the life, or shortening thereof, of a cartridge and, particularly a stylus.

In many cases, a moving magnet or moving iron with a "replaceable stylus" may not have an expiration date.  If the suspension holds up or a suspension is part of the replacement stylus, what is there to wear out that can't be replaced?

Most moving coil cartridges can have a new stylus and even a new cantilever installed of the suspension components and motor are still operational.

I recently had a new cantilever and stylus put onto a 20+ year old Lyra Clavis Da Capo with excellent results.  I will continue to use that cartridge with rebuilds when necessary.  That will continue until there is a more massive failure of the suspension or motor.  

Bpoletti is exactly right. The stylus is what wears out. On MM cartridges, the stylus is 95% of the total price of a new cartridge, and in some cases it’s actually cheaper to just buy a whole new cartridge if you shop around. Stylus profile has a lot to do with stylus lifespan, because of the size of the contact area. A conical / spherical profile will only be good for 300 hours, while a elliptical could go for 500, and a line contact 800 or 1000. Depending on how frequently you play records, you might need to replace the stylus because the bushings become dry and brittle from age before the stylus tip wears out.