As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
STARTER GENERATOR SPLINE SHAFT INSTALLED IN STARTER GENERATOR SHEARED AT THE BASE OF THE INTERNAL SPLINE AFTER ABOUT 25 START CYCLES. IT IS OUR OPINION THAT THE HOLE, WHICH IS DRILLED AND TAPE TO ACCEPT THE RETAINING SCREW IS BEING DRILLED TO DEEP AND IS THE CAUSE OF THE SHAFT FAILURES.