What was found
(CAN) A/C HAD UNCOMMANDED NOSE GEAR RETRACTION UPON LDG. IT NOTICED DURING POWER PACK PRESSURE TEST THAT 700PSI ON UP SIDE WHEN GEAR EXTENDING & THAT PRESSURE WOULD NOT DECREASE BELOW 50-100 PSI WHEN GEAR WAS FULLY EXTENDED.RESIDUAL PRESSURE PREVENTING DETENT PINS FROM ENGAGING. HYDRAULIC POWER PACK REMOVED & DISASSEMBLED. FOUND ONE 8 OF INCH OF BLACK SLUDGE & 1 X 5 INCH PIECE OF PAPER IN RESERVOIR.VALVE BODY ALSO DISSASSEMBLED. FOUND GEAR UP CHECK VALVE O-RING HARD & BRITTLE & SEATS OF MOST OF VALVES COVERED WITH SLIMY GOO. NOSE GEAR ACTUATOR DISASSEMBLED. MAIN PRESSURE O-RING MS28775-117 NOTICED TO BE ROLLED.