As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AFTER A CHANGE OF GEARBOX FOR ONE REMOVED SERVICEABLE FROM ANOTHER ENG, THE ENG STARTED LEAKING OIL IN FLIGHT, WHICH GAVE INDICATIONS OF OIL FLUXUATION. ENG WAS SHUTDOWN AS A PRECAUTION. SEAL WHEN REMOVED WAS FOUND FULL OF CARBON. SEAL WAS REPLACED, ACFT RETURNED TO SERVICE.