I'm not clear on which version of Penetrene each of you is talking about. Internationally Penetrene is a horse linament, made up of 80% acetone, 11% menthol, and the remainder a couple of plant-based skunk oils. In Australia Penetrene usually means an oil-based local proprietary penetrating and rust preventing liquid (though the horse linament version is sold here, probably causing some confusion at times).
Personally I wouldn't be putting acetone on any kind of plastic object I wanted to keep in one piece.
