This is a repost from FISD (by me)
learn a lot while restoring my ESB helmet.
I used several methods to remove the previous paint.
1) (wet) sanding
Takes a lot of elbow grease and takes ages. Also, you might lose some detail
2) "hair waxing"
apply some tape firmly to the paint, and then rip it off. Most of the paint will stick to the tape
3) Oven cleaning spray
yes. it works. Spray some foamy cleaning spray for the even onto the plastic. Let it work for at least 24 hrs. The paints gets "eaten away". Use a soft (tooth)brush to clean the rest. Repeat if needed.
It does not affect the plastic. Just the paint
Karin