Most, if not all, of those early "Z" Pentax's film advance motors had spindly plastic gears and often failed fairly early - uneven film spacing was common. If yours does have plastic gears, hopefully it hasn't had a lot of use, and you have a good return policy. It's pretty easy to remove the baseplate to check the gears, though I doubt that repair would be practical. Let us know how you get on with it when it arrives. Some of them may actually be of decent quality, but I don't know which ones. Good luck!