How'd you remove the mylar? I bought a 1977 Cleopatra playfield to tested a few methods. Freeze no good at all, but shellite and the a sunny day seemed to do the trick. I had a bit of paint loss in the beginning, but found that it was more due impatience. Lost little dots of paint in areas again from going too fast. Is that what you found or is it more a matter of luck of the draw?

The playfield still looks awesome and much better than before. The residue if its glue, you try to brush shellite like mad in areas to test if it comes up 

good luck with the project