I would go with the gasket material like the fist reply said. I had the same problem 2 years ago with my evinrude 18 hp with the two lines coming out of the tank and the pump on the top of the tank. It is almost impossible to find a replacement tank for that model so we have to keep maintaining the old ones until they are no longer with us. I took everything apart and lubed the pump and replaced the hose and put a new gasket from material I cut, on the top assembly. Works good as new, just have to keep it in good condition for another 35 years and we will have it made.
For my other evinrude, I just replaced it with the plastic tank. Plastic is better if you ask me. It doesn't rust and it is easy to see if you need more gas, esier to carry, doesnt scratch the boat bottom, and is a lot cheaper. I wish they made a replacement for the other evinrude I have. Talk later,
Magician