[Made to last]

Can anyone tell me how the Gas gauge works on a 33 ford It has a copper line running to the back of it. I learned from an earlier post that it is hydrostatically driven via air pressure. OK but is there supposed to be a column of fluid in the gauge itself that rises on the air pressure? Also when I removed the tank to overhaul, I was wondering what the Part is directly ahead of the spreader bar is. It looks like it takes oil and is leaking on one side. Some sort of torsion unit perhaps? Any help would be appreciated.