As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 5386 - LANDING GEAR DISAGREE MESSAGE WHEN SELECTING GEAR DOWN. NOSE GEAR DOWN AND LOCKED MAINS REMAINED UP AND LOCKED. FOLLOWED QRH, PERFORMED MANUAL EXTENSION. EMERGENCY DECLARED, AIRCRAFT LANDED SAFELY. REMOVED AND REPLACED MAIN LANDING GEAR SELECTOR VALVE.