40 gas tank?

[Kube]

Are you 100% certain the tank is leaking?
The design of these tanks made for common leaks at the filler tube rubber hose connection.
This is especially true if the tank was filled up all the way.

Before you remove the tank, do yourself a favor and track that leak down with certainty.

When I install a tank, I coat the rubber hose with Indian Head Shellac as directed on the bottle. Then I use modern clamps for a few days only replacing them with authentic clamps once the shellac has cured.