As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: DIRTY SOCK SMELL IN FLIGHT DECK, FIRST CLASS AND FRONT OF COACH ON DESCENT, APPROXIMATELY AT 6000' AFTER FIRST FLAPS WENT OUT AT 200 KNOTS. NO SMELL IN AFT OF AIRCRAFT. MAINTENANCE ISOLATED SOURCE OF ODOR TO THE APU. MAINTENANCE FOUND THE APU OIL COOLING FAN LEAKING INTERNALLY AND REPLACED IT PER AMM 49-52-51. A SATISFACTORY LEAK / OPERATIONAL CHECK WAS ACCOMPLISHED.