Something that doesn't melt the plastic.
I't try ALCOHOL first, and MINERAL SPPRITS second.
TEST on the backside before immersing.
I've used Easy-Off oven cleaner, as well as Castrol Super Clean (the degreaser, not the concrete cleaner) to remove paint. Both will strip the paint in short order. However, be careful with these chemicals--they can cause nasty chemical burns! Use tongs or latex gloves to handle the parts! Anyway, simply remove the locomotive's shell and spray it with Easy-Off, or let it soak in CSC. When the paint is gone, use an old toothbrush to scrub off any residue. Rinse off with warm water, and use dish soap if necessary. Two things I like about CSC, are that you can reuse it many times, and it doesn't stink up the house :)
I have an older Atlas C30-7 that I want to repaint. What works best to remove the old paint?
-Dave