I was biking in the city, in the rain today for about 5 hours. I noticed that my brake power was continually being reduced. Upon closer inspection of the brakes I noticed that a) There was grey crap all over the braking surface and b) that the breaks has lost several mm in profile since the morning. I really cant figure out why this would happen. The wheel isn't rubbing against the pads and this happened in the front and the back.