The only part that really deteriorates is the rubber gasket, which needs to form a seal to keep steam from escaping. Should be able to order a replacement gasket of the same size.
The rest is just mostly thick metal and can be cleaned appropriately.
Probably about a 30 minute job to restore it, I'm thinking? Assuming you can just soak it in some CLR or something. (a common commercial de-scaling and rust-removal product)
