What was found
BURNT OIL SMELL FROM AIR CONDITIONING WHEN NR 1 BLEED USED FOR PACK AIR SOURCE ON DESCENT. REPEAT GRIPE. RAN NR 1 AND NR 3 ENGINES TOGETHER AND SEPARATELY AS AIR SOURCE . RAN LEFT AND RIGHT PACKS TOGETHER AND SEPARATELY WITH BOTH PACKS ON. USING NR 1 BLEED, ABLE TO GET A HOT PACK SMELL (VERY SLIGHT) , BUT WERE UNABLE TO DUPLICATE DISCREPANCY. FOUND OIL IN NR 1 ENGINE 6TH STAGE SUPPLY DUCT AT PYLON. ENGINE REMOVED PER WORK CARD 70T005. REMOVED AND REPLACED ENGINE NR 1 PER WORK CARD 70T0005 AND 70T0301. RAN ENGINE. OPERATIONAL AND LEAK CHECK GOOD. OK FOR SERVICE.