As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON DESCENT "DIRTY SOCK" SMELL FROM AIR CONDITIONING SYSTEM. VERIFIED THAT THERE IS OIL SMELL WHEN USING LEFT AND RIGHT PACKS WITH THE APU AS THE AIR SOURCE. REMOVED AND REPLACED APU PER B737 800 AMM 49 11 00 400 803 ITEM G TO L (4) (G). RAN APU USING LEFT AND RIGHT PACKS APU WAS THE ONLY AIR SOURCE NO OIL SMELL DETECTED AT THIS TIME.