As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE TWO HOURS OUT FROM NRT RECEIVED -HYD Y RSVR LO LVL-, FOLLOWED COM AND AFTER ABOUT 10 MINUTES RECEIVED -HYD Y RSVR OVHT-. RETURNED TO NRT WITHOUT DECLARING AN EMERGENCY. LANDING WAS UNEVENTFUL AND AIRCRAFT TAXIED TO GATE. FOUND HYDRAULIC TUBE LEAK IN PYLON, REPLACED TUBE, ENGINE DRIVEN PUMP, FILTER AND CASE DRAIN FILTER. SYSTEM TESTED AND AIRCRAFT RETURNED TO SERVICE.