Ok. One more thing today. I dismantled the fuel gauge. The second picture show all the parts in order they were taken off. The hardest part was the rim. I guess there was a better way when it was new but I had to use some brute force basically. The rim holds the glass. Behind that was some kind of now totally hardened gasket. I wonder if I can find a substitute. Otherwise I will just use some silicone when I mount it.
Here are all the parts lined up. In center starting from the right are all the small things; the round nuts, contacts, insulators, washer, gasket etc. Then the rim and the glass. Bottom is the two clock-faces and the actual gauge. And on top the rusty casing and retainer.
The rusty backside of the gauge. The big hole is for the bulb.