As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APPROXIATELY 3.5 HRS INTO THE FLIGHT AT 0515 Z (ENROUTE TO OKO), PILOT ENCOUNTERED PROPELLER LOW OIL LIGHT. VISUAL INSPECTION CONFIRMED FLUID LEAKED AT NR 4 PROPELLER HOUSING. THE NR 4 ENGINE WAS SHUT DOWN AND AIRCRAFT RETURNED TO PLA. DURING THE DEFECT SIMULATION CHECK, HYDRAULIC FLUID WAS FOUND LEAKING FROM THE PROPELLER SHAFT HOUSING WHILE THE PROPELLER WAS SELECTED TO FEATHER POSITION.