ModelRailroaders use brake fluid to strip paint off of plastic shells - it softens the paint (you can remove it with a old toothbrush) but won't harm the plastic - but test it first before you throw a handfull of plastic ones to make sure, most of the model railroad plastics are styrene. - I just did this to some of my old spoonplugs that had paint that was attacked by plastic worms, stripped the paint right off.