Hi,
Generally we put lots of blood, sweat and tears into our minis. So, the very idea of undoing all of that hard work is a nightmare. I know because I'm doing this with a lot of mine. However, here are a couple of products I've used that have worked well for me and can be found at most hardware stores.
1. Goof Off 2 which works like magic on metals and they claim that it's safe on plastics. I HAVE NOT tried this product on plastic models, yet!
2.Simple Green is safe on both metal and plastic and works nicely.
Any questions just ask.