What was found
(CAN) CLIMBING OUT OF FL270, THE LT ENG LOST OIL PRESS & MASTER WARNING LOW OIL PRESS ANNUNCIATION WAS ILLUMINATED. AT REDUCED POWER OF ABOUT 55% N1, OIL PRESS INDICATED 78PSI. AT FLIGHT IDLE BOTH ENGS INDICATED NORMAL PRESS. INCREASING LT ENG POWER REDUCED LT ENG OIL PRESS. PRECAUTIONARY DIVERSION & UNEVENTFUL LANDING WAS COMPLETED. POST FLIGHT INSPECTION REVEALED NO OIL WAS SEEN IN THE SIGHT GLASS, MX REPORTED IT TOOK 5 QUARTS OF OIL TO RE-SERVICE THE ENG. FUEL SHUT OFF PLUNGER SEAL WAS FOUND TO BE DETERIORATED & CAUSED A LARGE OIL LEAK INTO THE EXHAUST AREA. REPLACEMENT SEAL IS ORDERED. MFG WILL INVESTIGATE TO ESTABLISH ROOT CAUSE & PROVIDE INFORMATION THROUGH SUBSEQUENT SERVICE DIFFICULTY REVIEW MEETING & SUPPORTING DOCUMENTS OR OTHER AGREED UPON COMMUNICATIONS.