As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: ON DESCENT WE NOTICED A MUSTY ODOR STARTING BETWEEN 10000 AND 15000 ORIGINALLY SMELLED LIKE A WATER SEPARATOR MELTING. WE HAD A LOT MORE CONDENSATION THAN NORMAL F/O SAID HE SMELLED A SLIGHT OIL SMELL DURING THAT TIME. COULD SMELL ON THE GROUND WITH APU RUNNING ALSO. MAINTENANCE FOUND APU OIL COOLING FAN LEAKING. REPLACED OIL COOLING FAN AND ACCOMPLISHED A SATISFACTORY LEAK / OPERATIONAL CHECK PER AMM 49-52-51-400-002A.