what to do ?

[HiperEX]

ok my rear disc in looking like rusty sort of i think it looks like rust or sumthing starting what should i do sand it off? use wd-40? i dont want to have ta buy a new one

[Quadfather]

Use brake parts cleaner, and one of those scotch brite pads, maybe finish up with some 120 grit sandpaper.

[4TraxRider]

Brake cleaner and the rough part of the two sided sponges.