What was found
(CAN) TURBINE ASSY WAS RECD IN FOR SMOKING ON SHUTDOWN. SMOKING WAS ENCOUNTERED APPROX 7 2NDS AFTER THROTTLE WAS ROLLED TO OFF POS.UPON DISASSY & INSPECTION OF PT SUPPORT IT FOUND THAT INNER DIAMETER (DIA.S) SHOULDER WIDTH WAS INSUFFICIENT FOR PROPER SEALING OF U-RING GASKET. AS A RESULT, THERE WAS A LOSS OF LABYRINTH SEAL PRESSURE & AN INCREASE IN AIR PRESSURE WITHIN POWER TURBINE SUPPORT OIL SUMP, ALLOWING OIL FROM 6 & 7 BEARING AREA TO ENTER GAS PATH. NOTE: SHOULDER WIDTH OF INNER DIAMETER SHOULD BE INSP TO ENSURE SUFFICIENT SURFACEAREA EXISTS FOR PROPER SEALING OF U-RING GASKET (PRINT DIM. FOR SHOULDER WIDTH UNAVAILABLE).P/N 6898731;S/N MK18387