What was found
AFTER TAKEOFF WHEN LANDING GEAR LEVER MOVED TO UP, L MLG INDICATED UNSAFE (RED). QRH COMPLETED THEN CYCLED LANDING GEAR, L MLG UNSAFE AGAIN. WHEN LANDING GEAR LEVER MOVED TO OFF THE L MLG EXTENDED (RED + GREEN LIGHTS ILLUMINATED). UPON THIRD ATTEMPT TO RAISE LANDING GEAR ALL GEAR INDICATED UP. GROUNDED - YES. PERFORMED GEAR RETRACTION TEST & FOUND LH MLG NOT FULLY RETRACTING. FOUND LANDING GEAR SELECTOR VALVE TO BE FAULTY. REMOVED & REPLACED LANDING GEAR SELECTOR VALVE REF AMM 32-31-51/401. PERFORMED OPS CHECK. OPS CHECK GOOD. NO ADJUSTMENT REQUIRED. GEAR PERFORMED AS REQUIRED NO FAULTS OR LEAKS NOTED. REF AMM 32-31-51-400-801. WHILE DOING OPS TEST GEAR FULLY RETRACTED AS REQUIRED ALL LIGHT INDICATION EXTINGUISHED.