Tough call...I would say either some Mineral Spirits or Denatured Alcohol should get it off. However, you need a coarse rag and lots of rubbing with those. The strippers that do it all without much scrubbing are usually bad for the plastic. You MIGHT try some JASCO stripper (though I can almost guarantee it will mess up the plastic), or some of this weird Orange-Citrus paint stripper stuff.