The most common wear is the Axl hole and the ball kickout from that. One of the most important piece to inspect is the proper ball launch wire form is present, and that topic has been beat to death here.
Parts are not impossible for this pin, and most of the mechanisms are shared by other Data East pins. Plastics are typically not broken, aside from the slings and the Axl hole pair, and those are all available from a sold out CPR repro (check ebay). The G ramp and snake pit ramps are both available, too (the pair is ~$200). The R(ed) ramp is not readily available, but it is seldom broken.
If it is missing parts for the gun ball launch, you could opt for the cheap replacement of a Last Action Hero one, or use a pair of real gun grips.
It is a good pin IMO, and one of Data East's best. If you dont like it, sell it.