What was found
DURING APPROACH, UPON SELECTING THE GEAR DOWN A GER DISAGREE MESSAGE WAS RECEIVED WITHOUT THE GEARS EXTENDING. THE QRH WAS COMPLIED WITH AND THE CREW MANUALLY EXTENDED THE GEARS SUCCESSFULLY. AN EMERGENCY WAS DECLARED AND AS A PRECAUTION IN CASE THE NOSE WHEEL STEERING DID NOT OPERATE PROPERLY. THE AIRCRAFT LANDED SAFELY AND WAS TOWED SAFELY TO THE GATE DUE TO THE NOSE WHEEL STEERING NOT OPERATING PROPERLY. MAINTENANCE REMOVED AND REPLACED THE MAIN LANDING GEAR (MLG) SELECTOR VALVE. OPERATIONAL AND LEAK CHECKS GOOD. AC OK FOR SERVICE. (K)