As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: SLIGHT MUSTY ODOR ON DECENT SIMILAR CRAYONS OR WAX THAT WENT AWAY WITH NO ACTION BEING TAKEN BY THE FLIGHT CREW. THE ODOR RETURNED AFTER LANDING DURING TAXI IN AND AT THE GATE. MAINTENANCE FOUND EVIDENCE OF AN OIL LEAK ON THE APU. MAINTENANCE REPLACED THE APU OIL COOLIING FAN THAT WAS LEAKING OIL PER AMM 49-52-51. A SATISFACTORY LEAK / OPERATIONAL CHECK WAS ACCOMPLISHED WITH NO ODORS NOTED.