[Steve Tinker]

Frodo - I've read on this board of new AOS units failing within a few hundred miles, so its one of those imponderables that can vary.
As with anything manufactured with plastic and "rubber" (nothing is rubber today), everything depends on exposure to max & min heat cycles, time, engine usage, acidic value of old oil attacking the plastic (as per IMS bearing seals), etc, etc, so I think your question cannot be answered easily.
Personally, if you check your oil cap vacuum weekly, look & listen for squeaking and smoking on startup and once a year inspect for excess oil and clean out the throttle body you won't go far wrong.
If there is no history of AOS replacement, THAT'S the time to replace it before it bites you on the a$$.