As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED A SHAKING FELT IN AIRFRAME DURING CLIMB AND CRUISE. MAINTENANCE INSPECTED AND FOUND THE #6 CYLINDER OF THE LEFT ENGINE TO HAVE LOW COMPRESSION. THE LEFT ENGINE RIGHT MAGNETO WAS FOUND TO HAVE INTERNAL OIL AND THE #1 CYLINDER IGNITION CABLE WAS FOUND TO BE INOPERATIVE. THE RIGHT MAGNETO, #1 IGNITION LEAD AND #6 CYLINDER WERE REPLACED.