[Aarongriffey]

I have three cars that I bought with dirty tanks. No problems with any of them in more than 20 years.
I cleaned two of them myself.
I put sockets, nuts and bolts and other metal pieces in the tanks and shook them around until all the crud was knocked loose.
Then rinsed them with hot water at the car wash. After they dried out I rinsed em with a little gasoline.
Here in taxafornia it was $175 to clean a tank, another 100 to seal it. I never sealed any of mine or had them sealed.
I think most good shops cut one side open and sandblast the inside of the tank before they seal it. If a new tank is available that is usually cheaper than monkeying around with the clean and seal headache.