Had one failure with a front exhaust stud before, a very tiny crack on the engine wall when I removed one of the 2 front down pipes. Found this stuff at local shop (2-component basis) that is basicly fluid 'metal' which is heat resistent and can be molded where it is needed...

http://www.bison.nl/NL/nl/view.do?UID=a ... dd2dc07c04

Also, a very cheap and basic stuff I use to get rusty bits off....use coke as in the soft drink you see everywhere (yes, the global known one with the red /white logo). Overnight soaked in this soft drink and you can pull it off

Phosphoric Acid etch will leave a hard, bright metal finish. This is because it will etch the surface slightly, exposing new, bare metal. Often this is desirable. It leaves an attractive surface and a surface ready to paint. A common product which contains Phosphoric Acid is Naval Jelly. The soft drink Coca-Cola contains Phosphoric Acid, so Coke will etch rust. But Coke also contains carbonic acid and other nasty things. You're going to drink that stuff?

above is quoted from here: http://www.metalwebnews.com/howto/rust/rust.html