What was found
ORD INFLIGHT T313 - FLIGHT ATTENDANTS REPORTED ELECTRICAL SMELL MIXED WITH SMELL OF BURNED PLASTIC. DECK NEAR AFT FLIGHT ATTENDANT JUMPSEAT SLIGHTLY WARM. BOTH AFT LAVATORY SMOKE ALARMS SOUNDED. AIRCRAFT RETURNED TO ORD AND LANDED WITHOUT INCIDENT. REPLACED AUXILLIARY POWER UNIT DUE TO LOW OIL QUANTITY INDICATIONS AND OIL LEAK AND RAN AIR CONDITIONING PACK BURN OUT. SYSTEM GROUND CHECKED NORMAL OPERATION.