It will happen to everyone's at some point. It's the glue they use. They are still one of my favorite figures. They look like they have been fighting ghosts. Lol I would sell them unless I had too. My Han though, I will try and fix with some clorox and water. I read someone fixed theirs by doing it.
I checked my figures last night and unfortunately mine have staining too. I live in Houston. It's the glue they used. They look battle damaged now. Lol