Only way to know is to run fuel dryer through there for a couple tanks, and hope it gets better.
Check the relay from the same point. Set to ohms, one lead on the wire, one to ground. Should read open (infinite) until the ignition is turned on, or the other way around. I forget. Anyway, it should change state with a change in state of the ignition switch.
What'* the resistance read when you can read through the pump? (not open circuit)?
Might be corrosion at the pump connector on top of the tank.