As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT RETURNED TO FIELD WHEN AFTER TAKEOFF THE CREW RECEIVED AN AFT LAVATORY SMOKE DETECTOR WARNING. MAINTENANCE INSPECTED THE AIRCRAFT AND FOUND OIL IN MIXING MANIFOLD AND VERIFIED THAT THE APU WAS LEAKING OIL. DUCTING WAS CLEANED AND MEL WAS CONTINUED. OPERATIONAL CHECKS WERE GOOD AND THE AIRCRAFT WAS RETURNED TO SERVICE.