My first choice would be brake fluid, because it usually only takes a few hours to soften the paint. Test a non-critical place to be sure. Second choice would be alcohol (denatured), however it may take days to soften the paint, depends on the paint. Alcohol will not fog or craze plastic. Third would be Super Clean cleaner degreaser or oven cleaner, both have the same chemical ingredents, however oven cleaner has a strong smell. Test a part first.