gear pins will shear if some debris gets picked up by the
oil pump, the slightest particle will cause a momentary shock to the pumps vanes and the shear pin will let go. if you have done any engine work, like gaskets or the like. this may be the source. the most common is the umbrella valve seals when they get old they become brittle and flake off particles. putting in a new gear is certainly a good thing but if it happens after that then a
oil pan removal may be needed to look for dirt