Any idea whether the pump even works? Do you know how old the pump is? If it's old enough to have the problem with the gears swelling, then you'll need to tackle that.
Check the hose and nozzle too and make sure the hose isn't cracked.
My fill line is kind of fussy. There's no good way to tell how full I'm filling it until it's actually full, but the line (or maybe the vent) must not be in great shape because I can smell gas when the tank is full. If I'm not going to be at camp soon to dispense some fuel, I'll turn the pump on and run a little bit of it out into a jug to bring the level down just a little.
Just curious, do you have a separate tank for your gen? Did the previous owner put many hours on the gen?