Make sure the ramps are in great shape. Replacements are unobtanium. In addition to looking for cracks, play a few games to make sure the ramps don't suffer from ball drops. I owned a PZ for a while and luckily experienced no ball drops. However I read about people here who had plenty.
Red rocket at the base of the left ramp is also unobtanium if missing. But that doesn't impact game play that much.