Hi y'all. Thanks for checking and weighing in some more.
I'll tell ya this about all that ^^ I'd love to just get the whole new water heater. In a former life, when $600 felt more like $250, I'd go for it. But this season of my life includes moments of learning rather than spending; in part because I do have the balance of time available to stretch my brain and learn about the inner workings of my house on wheels.
Even though it is leaking, it still works! It still heats the water on propane and/or electric power. We've used it a few times to heat up enough water to wash the dishes and take two showers while we decided what to do about it. The rest of the parts look wonderful. We've always been in nice climate. NO rust.
After we change out the water heater tank, I'm going to see how that Flex Seal would have worked on the old one. Have any of you used it yet?