rear wheel bearings repeatedly going bad

My 1991 300TE 4-Matic with 135K miles seems to be going through right rear-wheel bearings rapidly. Two new ones installed in 2 years, the second one already growling after 5 mo. Car recently aligned in a Mercedes dealership shop, 2 yrs ago. Had some freakish rear tire wear since, inner sides of tires suddenly exposing steel. New tires seem to be wearing all right. Car was once hit on right rear but not hard. before my 2 yrs of ownership. Have heard that the old 4-matics gave trouble. Mine so far works perfectly, but could there be some problem in the rear end or axles that causes wheel bearings harm? I feel no vibration, hear no other sound than the bearing growl, which starts at v. low speed and is not so loud at highway speeds. Superb car, but this is costing. By the way, I had both bearings put in by a small local VW guy. When one went bad, I surmised he might have damaged it in installation. Had a better shop do the second replacement and I know he took the carrier down and used a press, according to the instructions from my service CD or from alldatadiy.com. Would I be well advised to take it next time to a dealer's shop? Thanks for any help you can give! --mason

[Kestas]

Proper installation has a lot to do with bearing life. But you already had two different shops performing this repair, with the second one apparently being careful with his work.

Quality of aftermarket parts also have an influence on life of bearing repair.

It sounds like something is out of alignment, such as a bent part (bent knuckle?).