Mildew
The only thing that will effectively remove mildew is chlorine beach. Wear rubber gloves to protect your pinkies, then liberally dampen an old cloth with the bleach. Rub the bleach onto the plastic that is affected and the mildew will instantly disappear. Then IMMEDIATELY rinse or wipe the plastic very thoroughly. If you remove the bleach immediately, it will not harm the plastic.
Any of you who have G.E. Roll Easys are well aware of the "skin disease" these machines develop. Something about whatever kind of plastic they used to make the trim and attachments is an absolute mildew magnet. I had a nice Roll Easy that had ugly blemishes for years, figuring the white spots were a permanent disfigurement. Then Roll Easy expert Tania Voigt told me about the bleach deal and now my Roll Easy looks as good as new.