As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MIDWAY - FLT 168 - DEPARTED, MAIN HYDRAULIC SYSTEM PRESSURE FLUCTUATED AND THEN LOST PRESSURE. PILOT RETURNED TO MIDWAY. USED EMERGENCY LANDING GEAR HAND PUMP TO LOWER GEAR. LANDING WAS UNEVENTFUL. MECHANIC FOUND HYDRAULIC SYSTEM RELEASE VALVE LEAKING EXTERNALLY. REPLACED VALVE, LEAK CHECK SATISFACTORY, AIRCRAFT RETURNED TO SERVICE.