As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DFW INFLIGHT - CREW REPORTED SMOKE IN CABIN. RETURNED TO DFW AND LANDED WITHOUT INCIDENT. FOUND APU OIL IN PNEUMATICS. REPLACED APU ON 11DEC AT DFW DUE TO OIL LEAK. REPLACED BOTH LEFT AND RIGHT HEAT EXCHANGER AND CONDENSER. REPLACED BOTH LEFT AND RIGHT OZONE CONVERTER. SYSTEM GROUND CHECKED NORMAL OPERATION.