As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE TAXIING THE ACFT FOR MX, A MAGNETO CK WAS PERFORMED. THE RT MAGNETO WS ROUGH AND EXHIBITED A LG RPM DROP. THE DIFFICULTY WAS TROUBLESHOT, THE RESULT OF WHICH WAS THE DISCOVERY OF A DEFECTIVE MAGNETO. THE MAGNETO WAS REPLACED WITH AN O/H UNIT AND THE ACFT APPROVED FOR RETURN TO SERVICE. THE DEFECTIVE MAGNETO WAS A UNIT THAT HAD BEEN O/H AND HAD BEEN DELIVERED WITH THE ENGINE AFT REMFG.