i was gonna suggest the brakes.. usual way of testing is to spit on the disks (gross i know) to see which one is the hottest, or simply feel the temprature rise off the wheel. second suggestion was check tyre for bulge, but its not that ;)
I would consider looking for a transmission specialist or BMW specialist. Maybe aviod dealers at the moment. Get a diagnoses. Maybe it's a simple transmission fluid change and a ECU reset. I would not drive it about too much until you have had a specialist take a proper look.