So I managed to get the mylar off. The only thing I used was white spirit - thank you for the advice Retropin. Although I still need to clean up the remnants of glue left behind.
Early stages
Mylar now off
This area here was the one main part where I lost paint. I don't know why other than maybe the glue here on the mylar was stronger or something. This part was painful to remove compared to anywhere else. There was very little paint lost anywhere else in comparison except for here.
Have a look at this. See the big long white line in the black area. That was where whoever the clown was that put the mylar on went around cutting the edge of it to shape with a Stanley knife or something similar. There were a couple of other areas like it too.
One of the next jobs before touching up will be to start to address these things. Where I removed the wire guide rails quite a few areas the wood has "popped" up. I assume just sanding it flat then repainting is all I need to do? There are also lots of ball swirl marks around the top of the playfield I need to address. I read everyone talking about Magic Eraser as the best solution for these?
Any advice on how to get rid of the ball travel line in the shoot lane and at the top like this?