and tensioners fail (that's why it is recommended to change these at regular intervals)...can't say that I've ever heard anything about diff bearings failing. Sure, bearings are a wear item. Keep in mind that when designing a mechanical device it is possible to choose a tapered roller bearing such that it's lifespan in a given application will far exceed the useful life of the vehicle in which it is installed. Clearly, the R230 diff bearings fall into this category. So, unless they are obviously damaged due to contaminated lubricant, it is not necessary to change them.
:Thats my 2 cents. :)
No offense, but I value the opinion of a guy that rebuilds diffs for a living more than your 2 cents :) If he says my bearings don't need to be replaced, I'm going to take his word for it.