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 MUSTY SMELL IN FLIGHT DECK ONLY UPON STARTING DESCENT ALL THE WAY THROUGH ENGINE SHUTDOWN - MAINTENANCE FOUND THE APU GEARBOX VENT LINE HAD EVIDENCE OF COKING - MAINTENANCE REPLACED THE APU GEAR BOX AIR OIL SEPERATOR *AALA202609066516* AND THE APU VENT LINE ASSEMBLY *AALA202609063169* - A DECONTAMINATION OF THE ENVIRONMENTAL CONTROL SYSTEM WAS ACCOMPLISHED WITH NO LEAKS OR ODORS NOTED