As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - AFTER TAKEOFF CREW REPORTED SMOKE IN FORWARD PART OF CABIN. RETURNED TO ORD AND LANDED WITHOUT INCIDENT. FOUND APU OIL LEAK. REPLACED O-RING AND PERFORMED HIGH PRESSURE PNEUMATIC DUCTING BURN OUT. SYSTEM GROUND CHECKED NORMAL OPERATION.