It was the guage!

[Dave]

After the problem stopped being intermittent, and the failure sayed
with is for a while, we got a chance to nail this down, with an extra
tank sending unit to test it with..

Surprising enough, when the guage failed, the resistance was still
about the same as when it was working normally. I suspect a short in
one of the coils that operate the needle, that ocourred when the guage
heated up with operation.

Finally!

GRRRRRRRRRRRRRRRRR !!!


Dave