the oil pump shaft or the gear? You're gonna have to be a little more specific or show a picture, or do you mean the tiny metal piece that's on the plastic rotor?
With the rotor in place can you move the shaft side to side? I so the shaft bearing is shot and the rotor tabs are hitting the cap contacts and breaking the rotor tab.
Sounds like your dizzy is going out on you, so it wobbles, then the metal piece catches on your cap, so it breaks. Pull your dizzy out and see if the shaft has play