If you are worried about the amount of rust build up, get some penetrating fluid and spray the nuts liberally. Let the stuff work overnight. Then get a good socket and work the nuts loose then retighten the header with new nuts. You should be able to seal that leak. You can also remove the copper gaskets and reuse them. My headers have been off and on many times using the same copper gaskets, studs and nuts. Mines an 03.
