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 DIRTY SOCK, MUSTY ODOR COMING FROM THE AC VENTS WHEN APU BLEED WAS TURNED ON WHILE BOARDING THE ACFT AT THE GATE. MAINTENANCE FOUND OIL IN THE APU PLENUM AND REPLACED THE APU OIL COOLER IAW 49-91-44, THE APU OIL COOLING FAN IAW AMM 49-52-51. A SATISFACTORY LEAK AND OPS CHECK WAS ACCOMPLISHED WITH NO ODORS BEING NOTED. SEE AALA201607199012 FOR ADDITIONAL PART.