As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LHR - CREW REPORTED CENTER HYDRAULIC QUANTITY SLOWLY DECREASING ALONG WITH EICAS MESSAGE. EMERGENCY DECLARED FLIGHT RETURNED LHR LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. FOUND FLAP/SLAT SHUT-OFF VALVE MODULE IN RIGHT GEAR WHEEL WELL LEAKING. REPLACED MODULE. SYSTEM GROUND CHECK NORMAL OPERATION.