Coxy,
Not sure if I completely understand what's happening, but here are some thoughts:
if it looks like the tap is leaking fuel, check the threaded part of the tank that the tap screws to very carefully for leaks. This connection can develop internal cracks and since the threaded collar which is part of the tap is so close, fuel can run down the tap making it look like it is leaking. Try using a clean dry cloth to find exactly where the fuel is coming from. Can be tank connection, seal between tap and tank, tap lever seal, or filter bowl seal.
Not sure how this would be related to the fuel starving, that sounds like it might be a separate problem.
Good luck, these can be hard to find!