What was found
PDX - ON FLIGHT 2557, ON TAKEOFF RECEIVED A MASTER WARNING FOR SMOKE COMING FROM THE AFT LAVATORY. FLIGHT ATTENDANT NOTICED "HAZE" UPON OPENING LAV DOOR. AFTER A FEW MINUTES HAZE DISAPPEARED. RETURNED TO GATE. MAINTENANCE PERFORMED GVI OF ENGS NR 1, NR 2, AND APU FOR SIGNS OF OIL LEAKAGE. FOUND OIL IN NR 2 ENG 4TH STAGE AND AFT. REPLACED 4TH STAGE SOV ON NR 2 ENG. REMOVED AND REINSTALLED NR 2 SEAL PRESSURE REGULATOR VALVE. COMPLIED WITH COMPRESSOR WASH TO GET RID OF RESIDUAL OIL. OPERATIONAL CHECK GOOD. AIRCRAFT RETURNED TO SERVICE.