As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHIP 3239 - ATB/FUME - DIRTY SOCK SMELL IN CABIN AFTER TAKEOFF. AIR RETURN TO ATL. CORRECTIVE ACTION: FOUND APU OVER-SERVICED AND OIL LEAK AT OIL CAP, HOWEVER, NO OIL HAS BEEN INGESTED INTO APU INLET. BOROSCOPE OF ENGINES AND BLEED VALVES ALL CLEAN. PERFORMED REVERSE BURN AND ECS DECONTAMINATION. CLEANED APU INLET AND SET OIL TO THE CORRECT LEVEL. (2261269)