As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CABIN CREW REPORTED AN OILY ODOR WITH FAINT SMOKE IN THE CABIN SHORTLY AFTER TAKEOFF. EVENTUALLY IT ALL DISSIPATED, BUT THEN IT REOCCURRED WHEN THE APU WAS STARTED AT THE ARRIVAL GATE. MAINTENANCE FOUND THAT THE APU OIL CAP WAS LEAKING. THE OIL CAP WAS REPLACED, THE APU INLET CLEANED, A DUCT BURNOUT WAS PERFORMED, AND THE COALESCER BAGS WERE REPLACED. THE AIRCRAFT HAS RETURNED TO SERVICE.