What was found
AFT LAV SMOKE DETECTOR ALARM ON AND A BLUISH SMOKE IN CABIN WITH SMELL OF OIL. CABIN WAS CLEARED BUT SMOKE RETURNED. FOLLOWING LINE TROUBLE SHOOTING TO ELIMINATE THE APU AS THE OIL SOURCE THE SUBJECT ENGINE WAS REPLACED AND SENT TO THE ENGINE SHOP FOR REPAIR. INSPECTION SHOWED THAT OIL FROM THE NR 3 AFT CARBON SEAL HAD ENTERED THE GAS PATH THROUGH THE 10TH OR 14TH STAGE BLEED DUCT. THE ROOT CAUSE IS A FAILED 2/3 CARBON SEAL CAUSING HIGH GEARBOX BREATHER PRESSURE AND THE LEAKAGE PAST THE NR 3 AFT CARBON SEAL.