As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IMPULSE COUPLING FOUND TO BE CRACKED AT ADVANCE STOP NOTCHES OF BASE PLATE. DEFECT WAS DISCOVERED USING MAGNETIC PARTICLE INSPECTION OF PART DURING PERFORMANCE OF MANUFACTURERS RECOMMENDED-500 HOUR INSPECTION. HAVE SEEN THIS SAME DEFECT ON A VERY LARGE PERCENTAGE OF SLICK IMPULSE COUPLINGS USED ON 6 CYLINDER ENGINES.