Just had my 530 GT serviced at 17K. Exactly the same problem with threads showing on the inner edge of both rears. BMW are not interested, claiming i must have knocked the tracking out by hitting a pothole. I called BMWUK customer service who listened attentively, called the dealership and then called me back and repeated verbatim what the dealership had told me previously.
Waste of time BMW. I swore before i wouldn't by another BMW with run flats and i made the same mistake.