When checking the front brake pads on my K1300S,(48000KM) I found one of the four pads was worn down much more than the others.The wear indicator slots were down a bit on three of them, but non existant on the left outer pad. I was told this was caused by a build-up of brake dust and the piston was not returning properly. Could this be cleaned when the pads are removed without having to do a caliper rebuild ?