As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DESCENDING THROUGH 5000 FEET SOUR "DIRTY SOCKS" SMELL PRESENT IN FLT DECK. CONFIRMED APU IS THE SOURCE OF CABIN ODOR REF TASK 05 60 00 280 801C1. ALSO RAN BOTH PACKS WITH BOTH ENGINES. SMELL ONLY RETURNED WHEN APU WAS SELECTED. REMOVED AND REPLACED APU PER MM 49 11 00 400 803 AND TC 78349010. ACCOMPLISHED EA 800 05EA 04407. NO ODORS NOTED.