What was found
(CAN) UPON LANDING AT DESTINATION AFTER A 40 MINUTE FLIGHT. PILOT CARRIED OUT A WALKAROUND AND NOTICED AN UNUSUAL AMOUNT OF OIL ON TAILBOOM FROM BELOW TAIL ROTOR GEARBOX. OIL LEVEL WAS CHECKED AND WAS FOUND TO BE DOWN A LITTLE BUT STILL IN ACCEPTABLE RANGE LEVEL. UPON EXAMINATION BY AME INPUT SEAL TO GEARBOX WAS COVERED IN OIL. OIL LEVEL WAS DOWN 1/2 OUNCE FOR 4 HOURS OF FLYING. MAGNETIC SEAL WAS REMOVED AND EXAMINED AND IT WAS DETERMINED THAT THE CARBON RING OF THE MAGNETIC SEAL HAD A DEFECT. WHEN EXAMINED WITH A MAGNIFYING GLASS A TINY DIAGONAL CRACK WAS FOUND ON THE FACE OF THE RING. A NEW MAGNETIC SEAL WAS INSTALLED AND GROUND RUN AND FLIGHT TEST FOLLOWED. NO OIL LEAK EVIDENT AFTER FLIGHT.