As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLIGHT, APU OIL PRESSURE LOW LIGHT CAME ON AND APU SHUT DOWN. CROSSTIE RELAY WAS ON MEL. FLIGHT CREW RETURNED TO DEPARTURE AIRPORT. MAINTENANCE FOUND OIL LEAK AT FUEL CONTROL GARLOCK SEAL AND REPLACED SEAL. MAINTENANCE ALSO REPLACED AC BUS CONTROL PANEL. GROUND RUN AND CROSSTIE OPERATION NORMAL AND NO OIL LEAKS NOTED.