Bob --

I'd agree with the advice from both Ive and Don. The teeth on the starter drive gear didn't engage completely with the ring gear, and they began to wear on each other (sorta liked married couples.....).

The starter drive gear should be a separate item -- you shouldn't need a whole new starter motor.

A new ring gear from Volvo is going to cost a zillion dollars. However, if your car's an automatic, I know a good ring and flex plate from an older car will fit. I helped install one from a '72 140 in an '87 740 turbo -- fit perfectly, worked perfectly, cost nothing.

An old trick is to re-install a worn ring gear one bolt out of sequence. Because an engine always stops at one (of several) fixed locations, the worn spot ends up at a fixed spot. By rotating the ring gear slightly (wrt the crank) you can offset the worn spot and never be bothered again. Unfortunately, I don't think it's easy to do on a Volvo..... but check on it.

One final comment -- if you must pull the transmission to change the ring gear, be sure to install a new rear main seal at the same time. Even if yours is not leaking, the small extra expense is worth the peace of mind. Those seals usually start normal leakage at about 150k - 200k miles -- grab the opportunity to preempt another expensive headache.