As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: MUSTY ODOR FROM AIR CONDITIONING WITH BOTH ENGINE BLEEDS & APU BLEED ON BELOW FL 200. ISOLATED SOURCE OF ODOR TO THE APU. MAINTENANCE FOUND MINOR OIL LEAK FROM APU OIL COOLING FAN, REPLACED O-RINGS AND ACCOMPLISHED A SATISFACTORY LEAK / OPERATIONAL CHECK PER AMM 49-52-51.