What was found
FLT 210 - SMF-PHX - LANDING GEAR - SELECTED GEAR DOWN, WOULDN'T EXTEND, GOT ECAM & IMMEDIATELY GEAR EXTENDED, INITIATED GO-AROUND & BROUGHT GEAR UP, WHEN EXTENDED AGAIN GEAR WAS VERY SLOW TO EXTEND. REMOVED AND REPLACED MANIFOLD SELECTOR VALVE AND RIGHT MAIN LANDING GEAR DOOR ACTUATING CYLINDER IN ACCORDANCE WITH AIRCRAFT MAINTENANCE MANUAL 32-31-31 AND 32-31-35. NO DEFECTS NOTED.