As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EN ROUTE FROM NKW TO BAH. FLIGHT CREW NOTED MAIN HYDRAULIC SYSTEM FLUID QUANITY DECLINING. CREW FOLLOWED COMPANY PROCEDURES AND CONTINUED WITHOUT INCIDENT TO BAH. MAINTENANCE DISCOVERED O-RING LEAKING AT MAIN HYDRAULIC SYSTEM SELECTOR VALVE. REPLACED O-RING AND SERVICED HYDRAULIC SYSTEM IN ACCORDANCE WITH THE DOUGLAS MAINTENANCE MANUAL.