Just doing up an old set of shimano LX hubbed wheels with centrelock discs. The aluminium rotor arm part of the rear disc has some kind of corrosion, the black paint/anodising has bubbled up and underneath is some kind of white salt-like material. It scrubs off with a wire brush though, but I'm wondering if the integrity of the unit is still OK? The stainless steel pins holding the disc to the carrier are fine etc.
The wheel was used on a commuter bike so will have had salty water from winter roads on it frequently.