Where did my gauge fluid go

[FrankWest]

I think it evaporates, anyway this gas gauge is hokey at best.
10 years ago I purchased a new fuel line from Ray Nachize Spelling incorrect. But the fuel line was perfect, installed it and installed the fuel gauge line which was attached to the mail fuel line. Worked perfectly for several months then the fluid vanished. Either the fluid evaporates or back pressure causes it to drop back into the fuel tank?
Many people forget it and insert a red pip cleaner in the viewing tube.
I find it amazing that such a hokey device was actually part of the ford automobile.
I wonder what type of fuel gauge Packard and other high-end autos used during the same time frame.