As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AS THE ON GOING CREW AS SOON AS I WALKED ON THE AIRPLANE I NOTICED THE DIRTY SOCK ODOR. APU WAS ON, WITH THE PACKS. AIRCRAFT WAS GROUNDED. MAINTENANCE FOUND THE APU LEAKING OIL FROM THE STARTER AND REPLACED THE O-RING IAW AMM 49-42-51. A SATISFACTORY LEAK & OPS CHECK WAS ACCOMPLISHED WITH NO ODORS NOTED.