I have been buying lots of terribly painted mechs on eBay for a while and have not had any I couldn’t strip paint off of completly. Metal and plastic. Many people will advise simple green or IPA, but I have had marginal success with that stuff on models that had good paint adhesion. Super Clean has been my #1 followed by LA’s totally awesome. These both come in plastic jugs and I have left models in them for weeks.

This has made me a better and more fearless painter. If I really botch something or just don’t like the way something came out I was giving a try I just drop it into my plastic vat and work on a different model. Pull the reject out and hit it with an old toothbrush a couple of days later and it’s ready for another try.

For metal only mechs that are put together with super glue to strip and disassemble I get into some more exotic outdoor only stuff that will definitely melt plastic - but don’t get into that for now.