After looking at the playfield, I’ve determined that I will NEVER get all the dirt off of this thing. It’s pretty well burnt in. Other issues include chipping paint and wood near the plastic inserts, serious playfield wear near the pop bumpers and some slight discoloration.
The solution might be a complete playfield replacement. I’m still looking for one of the reproduction ones that Illinois Pinball made a few years ago. If I find one, it’s going to cost a lot to fix. So, while I wait for that to come around, I’m going to try cleaning it with every method I know.