As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW COMPLAINED OF A CABIN ODOR ISSUE (DIRTY SOCK ODOR) WHEN THE APU WAS STARTED, BEFORE BOARDING OF FLIGHT. MX FOUND SMALL LEAK OF OIL FROM APU OIL SCAVENGE FILTER HOUSING. REPLACED TWO O-RINGS. LEAK CHECKED OK. ALSO, REPLACED FWD CARGO SELECTOR VALVE FOR SUSPECT LEAK. ACCOMPLISHED DECONTAMINATION. NO ODOR NOTED AFTER REPAIRS.