6.4L is Notorious for leaks in connections in cooling system. After replacing an O-ring in OEM hose and getting a drip again in the same spot at bottom radiator nozzle it was time for a whole new hose piece. New Motorcraft hose came with an O-ring and a lock clip and new style white(on inside) sealing surface on rad side.
Recommend a 5 gallon bucket to drain the coolant into, you’ll fill it up for sure