Read everything here-

http://www.pinrepair.com/em/index.htm

Lubing is a not a good idea for that mini stepper unit. It will attract dirt. Many things can cause the score motor to cycle endlessly. For me, I had accidentally knocked the AX relay out of alignment. A maladjusted tilt switch on the game board or backbox will also do that.

Is this what you need?
http://www.flippers.com/catalog/product_info.php/ratchet-point-p-1628

or this-
http://www.flippers.com/catalog/product_info.php/a9016a8933-p-1630

Ditto on PBR. I have bought a lot of things from Steve and his prices are good. The shipping cost from Flippers is expensive, so I would only go to them if PBR doesn't have what you need. I asked Steve at PBR if he had the ratchet shaft and he said he didn't. This was a few months back.