What was found
PILOT REPORTED NO LT GEAR DOWN LIGHT, AND GEAR SELECTOR HANDLE WOULD NOT RETURN TO NEUTRAL BY PILOT AND AIRCRAFT WAS ROCKED. GEAR DOWN LIGHT CAME ON AND AIRCRAFT LANDED. WHEN CHECKING FOR CAUSE HYD FLUID WAS FOUND COMING FROM LT ENGINE HYD PUMP DRAIN. AIRCRAFT RETRACTION TEST WITH HYD TEST UNIT WAS NORMAL. REPLACED LT ENGINE HYD PUMP, RAN ENGINE AND PRESSURE CHECKED SYSTEM BY OPERATING GEAR SELECTOR HANDLE TO DOWN POSITION, INDICATING GEAR HYD SYSTEM PRESSURE, OK. A FLIGHT TEST WAS DONE AND GEAR OPERATION WAS NORMAL. PROBABLE CAUSE WAS AIR GETTING INTO SYSTEM FROM LEAKING HYD PUMP AT SHAFT SEAL.