Glad to see Witt; Alfred and in the past, Al Lieffring on board the "replace the old fuel tank".
MOSTLY, (not all the time) a 40+ year old fuel tank can not be made to work properly or reliably on these cars. Witt discovered it; I discovered, and so did Al Lieffirng.
Time spent on trying to repair a tank is time wasted; usually money wasted too. While this waste is going on you don't have access to your car, and while your back is turned the price of a new tank (or repro) is going up...
The choice is yours. After struggling for several years with the nasty results of an old fuel tank I took the advice of a "Meistermechanik" here in Michigan who worked on the Pagoda assembly line, and replaced it. Have not looked back.
There are so many OTHER things to worry about!