I noticed that one of the rear discs on my M5 is corroded, like the brake hasn't been used. My first thought was that the pad is too low (there are two thin strips that aren't corpses) or the caliper is sticking.

Took it to the dealer for confirmation and one of the guys from the service desk had a kook and said that it was corroded and the pad was 'riding the corrosion.....sounds like bollocks to me. Now the car is under extended warranty, so if its just worn discs its not covered, but if its a caliper that's caused it then it will be covered and they will have to put new discs on it under warranty.

What do you think? I might just take the caliper off and have a look at the pads myself. The service computer is saying 8k miles left on the pads.....is this just based on how many miles you have done?