As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APPROXIMATELY ONE HOUR INTO FLIGHT, NUMBER FOUR HYDRAULIC QUANTITY DROPPED TO 2.4 GALLONS. FOLLOWED QRH PROCEDURES BY TURNING PUMPS OFF. FINISHED QRH PRIOR TO LANDING. FOUND NR 4 HYDRAULIC RETURN LINE LEAKING. REPLACED NR 4 HYDRAULIC RETURN LINE IAW B747-AMM 20-50-01. LEAK CHECK GOOD, NO DEFECTS NOTED.