As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE IN CRUISE, THE NR 4 ENGINE OIL QUANTITY DROPPED TO ZERO. OIL PRESSURE FELL TO THE YELLOW BAND AND THE ENGINE POWER WAS REDUCED TO IDLE FOR TWO MINUTES. THE ENGINE WAS THEN SHUT DOWN. MAINTENANCE FOUND A COVER ON THE ENGINE ANGLE GEARBOX LOOSE. THIS WAS CAUSED BY A GEARBOX BOLT HELI-COIL INSERT THAT HAD BACKED OUT. THE GEARBOX WAS REPLACED.