What was found
(CAN) THE FLIGHT CREW REPORTED DURING CRUISE: WHEN FOLLOWING THE QRH PROCEDURES FOR A MLG OVERHEAT FAIL MESSAGE . THE GEAR DISAGREE WARNING MESSAGE ILLUMINATED. THE A/C COULD NOT CONTINUE THE FLIGHT WITH GEAR SELECTED DOWN DUE TO THE MLG OVERHEAT FAIL MESSAGE & THE ADDITIONAL FUEL REQUIREMENT. AIRCRAFT RETURNED TO THE DEPARTING AIRPORT & DECLARED EMERGENCY. MAINTENANCE REPLACED THE NOSE & MAIN LANDING GEAR PRIORITY VALVE. AIRCRAFT RETURNED TO SERVICE.