Many old machines have a film of dirt and cigarette smoke over everything.
I've had good luck cleaning playfield plastics and plastic score reels with
Dow "scrubbing bubbles" bathroom cleaner. I do not spray it directly on the
machine, instead I apply it with a cloth or paper towel. You should let it
sit for a minute to soften old grime before wiping off. As with any
cleaner, you should try it on a small, inconspicuous spot first to make sure
that it does not damage inks or decals.