What was found
PILOT REPORTED THAT GEAR FAILED TO RETRACT AFTER TAKEOFF. AIRCRAFT RETURNED TO AIRPORT AND WAS INSPECTED. FOUND HYDRAULIC FLUID TO BE CONGEALED AND CONTAMINATED IN PUMP RESERVOIR. SENT PUMP OUT FOR OVERHAUL. FLUSHED ENTIRE HYDRAULIC SYSTEM TO REMOVE CONTAMINATED FLUID. RE-INSTALLED OVERHAULED PUMP AND RE-SERVICED SYSTEM WITH NEW MIL5606 FLUID. PERFORMED GEAR OPERATIONAL AND LEAK CHECK, FOUND OK. SUBMITTER RECOMMENDED FLUSHING HYDRAULIC SYSTEM AND REPLACING FLUID AT 5 YEAR/1,000 HOUR INTERVALS TO COINCIDE WITH 5 YEAR/1,000 HOUR FLEXIBLE FLUID LINE CHANGE.