If, as I suspect, the problem is in the pickup tube, don't be fooled if you see a tube that extends nearly to the bottom of the tank, as you might with a flashlight, or a flashlight and a mirror. Mine looked whole, but when I unsoldered it and pulled it out, it had a largish pinhole corroded into it that was invisible from the sender mounting hole. BTW, I cut the tube at that point and soldered on a piece of copper refrigeration tubing.
Bob S.