What was found
(AIRCRAFT GROUNDED) DURING DECENT THROUGH 15,000 FEET, DIRTY SOCK ODOR BECAME APPARENT IN THE FLIGHT DECK. FA/S IN FWD AND AFT ALSO SMELLED TH EODOR. PERFORMED ELIMINATION OF ODOR/FUMES IN FLIGHT DECK/CABIN QRH PROCEDURE. WITH PACK 1 OFF, ODOR DISSIPATED BUT RETURNED WITH PACK 1 TO ON AND PACK 2 OFF. WITH PACK 2 OFF ODOR DISSIPATED BUT RETURNED (IN AFT CABN) WITH PACK 2 ON. / WHILE PERFORMING LVL 1 TASKCARD FOUND OIL ON APU INTAKE SEAL AND INTAKE PLENUM, FURTHER TROUBLESHOOTING IN PROGRESS"