A quick addition here. I'm restoring a TZ and the balls were in torrid condition and the powerball looked like a ball of coal and stained beyond salvation.
Well... Overnight in the tumbler with some walnut media & Flitz and they look brand new! The powerball looks perfect. One of the pinballs has a chip in it so I will chuck it but the rest look like they were just produced.
Definitely worth a try IMO to "refresh" your, ummm, balls.