As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: FLIGHT CREW REPORTED A REPEAT ODOR THAT OCCURRED IN DESCENT 13000 TO LANDING MUSTY SMELL, ACRID QUALITY TO IT ON ROOF OF MOUTH. IN CLEAR AT IDLE HP VALVES CLOSED AND UP VALVES OPEN. MAINTENANCE FOUND THE APU HAD BEEN PREVIOUSLY OVER SERVICED RESULTING IN THE APU BEING CONTAMINATED. MAINTENANCE CLEANED THE APU PLENUM, INLET AND LOAD COMPRESSOR PER AMM 49-00-00 AND AMM 49-20-00. A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED WITH NO ODORS NOTED.