What was found
(CAN) ENGINE OIL WAS DETECTED COMING THROUGH THE UPPER AFT RT SIDE INTERIOR PANEL AND GRAVITY LEAKAGE DOWN TO THE AIRCRAFT FLOOR. THIS CONDITION ONLY EXSISTED UNDER STEEP RT TURNS OF THE HELICOPTER. AIRCRAFT RETURNED TO BASE AND UPON INVESTIGATION, IT WAS DETERMINED THAT THE RUBBER OIL SEAL FROM THE ENGINE OIL FILLER SUPPORT TO ENGINE OIL TANK, DEVELOPED A HOLE UNDER THE CLAMP AT THE TANK. OIL TANK IS LOCATED AT THE UPPER RT (AFT FACING FORWARD) OF THE MD 500D HELICOPTER. NEW SEAL WAS INSTALLED AND THE AIRCRAFT WAS GROUND RUN AND FLOWN WITH NO FURTHER LEAKAGE.