What was found
(CAN) WHEN THE CREW SELECTED GEAR DOWN FOR LANDING THEY GOT A GEAR DISAGREE MESSAGE. THE MAIN GEARS WERE DOWN AND LOCKED BUT THE NOSE GEAR WAS STILL IN THE UP LOCK POSITION. CYCLED GEARS 3 TIMES WITHOUT SUCCESS. MANUAL EXTENSION WAS PERFORMED AND CREW GOT ALL THREE GEARS DOWN AND LOCKED. ACFT WAS BROUGHT INTO A HANGAR AND NLG GOT INSPECTED BY NFF. MAINTENANCE DECIDED TO REPLACE THE NOSE GEAR SELECTOR VALVE AS A PRECAUTIONARY MEASURE.