As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED INOPERATIVE RIGHT MDG ON LEFT ENGINE. UPON INSPECTION OF MAGNETO, THE CONTACT ASSEMBLY WAS FOUND TO BE THE CAUSE. THE TWO RIVETS THAT HOLD THE CAM FOLLOWER ONTO THE CONTACT ASSEMBLY WERE LOOSE. ITLOOKS LIKE THE SLOT HEADS HAVE WORN INTO THE CAM FOLLOWER MANUAL.