As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DISCREPANCY: AIR TURN BACK DUE TO LOSS OF #4 HYDRAULIC FLUID. 50% REDUCTION IN 2 HOURS OF FLIGHT. CORRECTIVE ACTION: UPON ARRIVAL AT GATE ALL FOUR HYD SYSTEMS WERE IN THE GREEN BAND. PERFORMED LEAK CK ON #4 EDP AS PER AMM 29-11-08, NO LEAKS NOTED.