a very fine grit sandpaper, used very gently with water .. i'm talking FINE F INE FINE sandpaper like the kind they use as a final sanding on car paint kind of fine ... very careful work with an x-acto blade can help remove some of the flakey chunks ... acetone doesn't like many SW figures ...
as for the glossy aspect, it really depends on when the figure was released, what set it was released in, and what wave/series it was in.