Sending Unit Repair
Thanks to Brian H. (6m459) for this excellent article.

I measured my sender unit resistance and found it to be open circuit as was suggested by another member.

I removed it from the tank to find that the wiper would loose contact with the resistance wire at the mid point, of the float travel, as the resistance wire substrate is warped. It made good contact at top and bottom but not in the middle. I found that there is a handy adjustment available that lets you re-tension the wiper quite easily. Undo the screw and slide the bushing closer to the resistance wire, against a compression leaf spring, then re-tighten the screw. All seems to work well again now but I'll be keeping a close eye on it for the next little while.

Shown with cover removed. Note bend in resistor wire substrate.

The wire loses contact with the resistor midway.

Solution: Loosen screw, slide wiper closer, retighten.

Close up view.