As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DFW INFLIGHT T351/22AUG. AFTER TAKE OFF FLIGHT ATTENDANTS REPORTED BLUE HAZE COMING FROM AIR CONDITIONING. RETURNED TO DFW AND LANDED WITHOUT INCIDENT. REPLACED AUXILIARY POWER UNIT (APU) DUE TO OIL SATURATING APU COMPARTMENT. SYSTEM GROUND CHECKED NORMAL OPS.