What was found
DURING A CHECK-FLIGHT, THE EMERGENCY GEAR HANDLE WAS PULLED. THE GEAR EXTENDED, BUT THE HYDRAULIC POWER PUMP KEPT, AFTER RETRACTION, PUMPING AND CYCLING. THE CIRCUIT BREAKER WAS PULLED TO KEEP PUMP/MOTOR FROM OVERHEATING. ON THE GROUND, THE LANDING GEAR RETRACTED, BUT THE PRESSURE WENT DOWN TO 1000-600 PSI. AFTER REPLACING THE VALVE ASSY, THE SAME THING HAPPENED AFTER AN EMERGENCY EXTENSION. WHEN THE VALVE ASSY LANDING GEAR SELECTOR WAS DISASSEMBLED, FOUND THE O-RING RUPTURED. SUBMITTER SUGGESTS TO HAVE THE HOUSING HOLES DEBURRED, A BETTER O-RING, OR EVEN BETTER - A NEW AND BETTER DESIGN.