If it seemed to go on and off, seemed to read correctly when it was on, there's a broken current path somewhere. These instruments have their steel mounting posts swedged into a weak fiber board. So a weak pal nut was used to secure the post to the printed circuit board. So yeah a pal nut is part of the current path. Over time, the materials distort, vibration effects, those nuts can get loose. If fuel gauge is the only part of the panel that doesn't work, I would first find that sender signal wire behind the left kick panel and test there.
If I must pull the panel, I'll clean and tighten all contacts, bench test everything, add a chassis ground wire, all new light bulbs, do it all and be done with it.
