Glad you were able to find the exact problem.
Its often one of the small fuel hoses on the sending unit that are cracked and seeping, since there is usually three (feed, return, vent) attached to the sender for each tank. If you have dual tanks, you also have a 6 port switching valve with six more short hoses. The hoses at the switching valve are even more prone to leaking, since its mounted lower and fuel tends to pool in the hoses.
I plan to go through my truck and replace all small rubber fuel hoses with fuel injection hose and full circle hose clamps. The old rubber hoses do not last very well with the new gas that is part ethanol.
Bruce