What was found
EN ROUTE, AFTER TAKE OFF WITH LANDING GEAR UP RECEIVED A LEFT MAIN GEAR UNSAFE LIGHT. LOWERED GEAR DOWN AND RECEIVED UNSAFE ON BOTH MAIN GEARS AND GREEN ON NOSE GEAR. RAISED GEAR AND RECEIVED UNSAFE ON LEFT MAIN LANDING GEAR AGAIN. RETURNED, LOWERED LANDING GEAR DOWN WITH ALTERNATE SYSTEM, LANDED WITHOUT INCIDENT. REPLACED LEFT HAND MAIN GEAR RETRACT ACTUATOR. SWUNG GEAR, SYSTEM GROUND CHECKED NORMAL OPERATION.