Sounds like a late Marelli bike as the early ones had screw in fittings and Delphi's only have one line. They have an O ring. Sometimes just removing the line and reconnecting it fixes the leak, strange it would be on the return side as it normally has very little or no pressure.
The fittings in the tank have check valves in them, they often don't work but they have them, no need to drain the tank to take a peek, if they work.
The fittings in the tank have check valves in them, they often don't work but they have them, no need to drain the tank to take a peek, if they work.