Frank, I've often assumed the worst when carrying out a repair, done the extensive repair, and then found it was not the problem after all. Back in 1965
the clutch failed on my first car (1956 Austin A30 van). I spent a dreadful week in January, learning how to remove a gearbox while lying in a layer of melting ice. I installed a replacement clutch, (which, as a student, I couldn't afford without giving up lunch for a couple of weeks), and then reinstalled the gearbox. As I did so, I noticed that the clutch pedal pivot rod had dropped out of the frame when a split pin had corroded away. A whole week wasted.
So, for your fix, I would look for all possible simple solutions. One possibility is that the hose from the external filler to the tank has split. Another is that the hose clip where that pipe meets the tank requires tightening. Another is that frost has split a couple of pipes. Another is that a drain valve has been left open. I have had all four of these issues at various times over the past 8 years. Only if all these other causes have been eliminated would I look at the tank. Good luck with the hunt.