Originally Posted by wizardPC
Any XJ will have a cracked exhaust header unless it's already been replaced. That wont affect operation or emissions.
I'd be more worried about the "some rust"
Not every xj has or will have a cracked header, it should make you run rich because now your o2 sensor will be out of wack, and depending on its size it may annoy the hell out of you or the cops in your area...
Welding the leak is usually a temp fix, I suggest replacing it yourself otherwise its going to cost you quite a bit at a garage, and really its pretty easy, just time consuming