What was found
DFW/CUU - FLT 445 - AFTER TAKING POSITION ON THE ACTIVE RUNWAY AND PRIOR TO TAKEOFF ROLL, CREW RECEIVED A 'PROXI LOCK FAIL' AND 'PROXI HYD FAIL' EICAS MESSAGE AND CAUTION CHIME. CREW CANCELLED TAKEOFF CLEARANCE AND TAXIED OFF RUNWAY AND BACK TO GATE. PROXI PROBLEM RECURRED TWICE EN ROUTE TO GATE. DURING T/S MAINT REMOVED CANNON PLUG ON RT GEAR DOWNLOCK AND FOUND IT CONTAMINATED. MAIN CLEANED OUT DEBRIS AND RE-INSTALLED CANNON PLUG, PEROFMRED PLUG, PERFORMED OPS CHECKS AND TAXI CHECKS, ALL SATISFACTORY IAW MFG MM. ACFT RETURNED TO REVENUE SERVICE.