BMW will blame your cleaning, say you put the bike away wet etc, in reality its just the real crap quality of the BMW anodizing and coating.
One year old and Im losing the anodizing off the swing arm round the chain adjusters and round the spoke to hub holes. The brake bolts are rusting and the banjo bolts and hose fittings are looking poor.
Since the early 80s BMWs quality has become much worse. At the same time the cost of their bikes has fallen by about 30% making them affordable and comparable with other manufactures.
I can understand the reasoning but don't like the way some corners have been cut to make them affordable.
You don't say how old the bike is, if its only months old take it back to the dealer and try for a new wheel, my dealer is sympathetic but big warranty changes require authorization from BMW UK.