I just bought a 1952 Gottlieb Hit N Run wood rail in pretty nice shape. The playfield plastics are pretty curled, though. I've straightened SS and 60s-70s EM plastics using the oven for 5-7 minutes, slide in a big book and flatten technique. Is this the right technique for these too? At first touch they feel a bit more brittle than the later ones. I'd really hate to break one!
Here's a pic of one of the plastics: