As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
JUST PRIOR TO AIRCRAFT BEING INDUCTED FOR 100-HOUR INSPECTION, PILOT INFORMED MAINTENANCE OF ROUGH RT MAG ON RT ENGINE. INVESTIGATION SHOWED SEVERE CORROSION ON POINTS, GEARS, CAPACITOR, AND BEARINGS. CHECK REMAINING 3 MAGNETOS AND FOUND IDENTICAL CONDITIONS OF SEVERE CORROSION. ALL FOUR MAGNETOS WERE CLEANED AND AFFECTED PARTS WERE REPLACED. PROBLEM BELIEVED TO BE CAUSED BY PRESSURIZED AIR FROM TURBOS.