As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER LANDING, ON POST FLIGHT WALK AROUND, DISCOVERED OIL PRESENCE FROM ENG DECK DRAIN UNDER ACFT. UPON OPENING ENG COWLING IT WAS DISCOVERED THAT THE OIL PRESENCE WAS ON THE ENG DECK & LEAKAGE APPEARED TO BE COMING FROM THE BASE OF THE ENG OIL FILTER CUP HOUSING FROM THE O RING SEAL. REPLACED THE OIL FILTER CUP O RING ON THE ENG. GND RUN WAS COMPLETED TO CONFIRM THE DISCREPANCY HAD BEEN CORRECTED & THE ACFT WAS RETURNED TO SERVICE.