On 12/2/2012, David Benyon in Bude, Cornwall wrote:
"You forgot to mention the arc welder method. This can be extremely useful when a bolt or stud has snapped off flush with the casting. In this case obtain a piece of steel strip and drill a hole at one end. The hole needs to be the same diameter as the rusted bolt or perhaps a little larger. Put the hole over the broken stud. Using plenty of current blast down into the hole. Once the metal has turned from red to black try to unscrew the bolt. Usually the weld will fail but that was only the first attempt! Keep on drilling holes and blasting down with the welder and after a few tries the bolt will come out. It seems to be the intense heat that decomposes the red rust to black iron oxide which is smaller.

"One trick that I have used in the past is what I call "wet bolting". If one is putting a screw into a captive blind nut it is a good idea to slap some Duracote Anti Corrosive Red Oxide onto the bolt and down the hole. The paint seals-up the threads which would otherwise form a spiral groove for the wet to get in. Volvo used to use a special compound on the screws that held on the front wings of the Volvo 145. It was a gooey non-hardening paste. Even when the cars were 20 years old it was easy to replace a wing".