Same thing happened to my Mallory Unilite. I was using a standard volume standard pressure pump.
Take a close look at the bottom of your gear. Do you see a wear mark on it? The gear is coated with something black, so if it's not completly black, it's rubbing.
That slight bit of rubbing on the bottom of the gear pressed upwards just a little bit. Eventually, that upward pressure sheared the pin. Not related to the
oil pump at all.
Before you re-install the gear, grind off that little step on the bottom.