I've been using some stuff called "RestorIt4", it's made for cleaning calcium and lime deposits. It's mostly a weak phosphoric acid and I've used it on two of my prewar sets. To see the before and after pictures of the chassis go to my web page (
www.myvintagetv.com) and go to either the TRK-12 or TRK-5 restoration page.
It won't do anything for rust, that you'll need to use wire brushes and lots of elbow grease, but for oxidization and crud it works great.
Chuck