What was found
UNCOMMANDED LT MLG EXTENSION IN FLIGHT AT 315 KNOTS. REDUCED AIRSPEED AND REDUCED ALTITUDE. CORRECTED SEVERE YAW. SELECTED GEAR DOWN, 3 DOWN & LOCKED. CONTINUE TO DESTINATION. FLY-BY CONFIRMED GEARS DOWN AND PERFORMED A SAFE LANDING. JACKED ACFT, AND TROUBLESHOOT TO FAULTY INTERNALS, TIGHT ACTUATING PISTON IN MLG SELECTOR VALVE. REPLACED LANDING GEAR SELECTOR VALVE, GEAR SWUNG MULTIPLE TIMES, COULD NOT DUPLICATE MAIN GEAR UNCOMMANDED EXTENSION. SERVICED HYDRAULICS AND RETURNED ACFT TO SERVICE.