Freezing mylar off Segas works great! They were clearcoated pretty nicely, so you don't have to worry about art or paint coming off if you use the freeze method. I froze off my A13 mylar...and there's a beautiful brand new shiny clearcoat under it. I also froze the mylar off my Austin Powers when I had it...Stern game, I know...but right on the tail of the Sega years, so - same thing, really.
Now - keep in mind these games had mylar for a reason. A13 because of the 13 ball Multi, Austin Powers due to the laser-cannon shot, and Frankenstein due to Frank throwing the balls. So, even though I took off the dingy mylar, I put a nice shiny piece right where the balls all dump out on A13 to protect that area. I'm not sure if Frank always throws the ball to a similar spot....but if so, it might be good to just put a small new mylar piece there.