As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB NR 4 HYD SYSTEM STARTED DECREASING AND LOW QUANTITY LIGHT CAME ON. FHB PROCEDURES C/W AND QUANTITY WAS STILL DECREASING. ENG PUMP SWITCH WAS POSITIONED TO "SUPPLY OFF" WITH ENGINE RUNNING. QUANTITY INDICATOR ZERO AT COMPLETION OF CHECKLIST. FOUND HYD FLEXLINE AT LEFT WING GEAR DOWNLOCK ACTUATOR ASSY UNLOCK LINE LEAKING. REMOVED AND REPLACED HYD FLEX LINES PER GMM 7.4.1. REMOVED AND REPLACED NR 4 HYD PUMP AND CASE DRAIN FILTER AS PER AMM 29-11-03/05.