Repeat Differential Failures
Been lurking for a while, but I am stumped, so here's a FP.
I have a '03 325i with about 93,000 miles. In August 2011 we were travelling out of state and driving up I-95 in CT when we heard a loud whirring noise, shortly followed by a clunk and lost all power to the wheels. Getting into the break-down lane was exciting to say the least.
AAA towed us to a local shop, and they diagnosed a total failure of the rear differential. It also managed to take out the rear brake calipers. We secured alternate transportation while the shop put in a used replacement.
That October, I take the car in for yearly PA inspection at my local shop. They notice the new differential is leaking fluid. I call the CT shop to get a part under warranty. That ordeal is a separate story, but the result is this March (2012) I had yet another replacement diff put in, and all seemed fine.
This weekend (October 2012), the car again broke down. Similar story to last August, but at least this time we're local. My shop confirmed this afternoon that the differential failed again.
The shop guy thinks it must be something about my vehicle that's destroying these diffs. The car doesn't see much driving besides weekend trips out of the city and quick jaunts to the store, and I'm a pretty defensive (read: boring) driver.
The only other contributing fact I can think of is I had a low-speed rear collision about two years ago (Summer 2010), and they had to replace the rear bumper and the lower trunk frame. I can see that maybe causing misalignment in the drive-shaft, but would that result in the diff going?
I'm probably going to have the repair done regardless ($300 for the part, ~$400 labor), since it doesn't have much trade-in value otherwise. But anyone have an opinion as to the underlying cause of these failures? Should we just give up and start shopping for a replacement? ($900 every 9 months is still cheaper than a car payment).