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I'm not a fan of the tank sealers. I'd give a go with some Evapo-rust or such first and see how it looks after a couple of go rounds with that. Decent chance that adding a pencil filter in the fuel shut off after using the Evapo-rust would do the trick.
If you have a build up of varnished fuel in the tank put in a couple quarts of carburetor cleaner and slosh that around and rinse first before using a rust dissolving solution.