Thank you. I've wondered about this for years. I was visiting a tool forum many years ago when someone wanted to put a new motor and compressor on an old air tank. Even if you drain moisture regularly, rust occurs. At what point is a tank too rusty to save? I would only bet on say a 5 year old lightly used compessor for my needs. I'd stay away from anything used for years in a commercial / industrial environment or a "barn find".