I've got the same problem. Purchased a BMW Premium Selection Vehicle from BMW Melbourne, and have had a string of problems with the car, culminating in the diff packing it in at 100k.

Repairs costs have varied from $4700 at Euroserv Killara (Sydney North Shore) and $8000 at BMW North Shore. Wait is three weeks for part which needs to be shipped from Germany. They have run out of these parts in AU, which would point to the problem being more common than an aberration.

Symptoms in my case were jerking (as if you were driving a manual and didn't have enough revs before releasing the clutch) when accelerating from a standing start. Gradually got worse to the point where it was making a loud clunk, then grind, then the whole thing stopped.