So i just purchased my XJ around 2 weeks ago, seeing how im broke its sitting in my driveway i've been doing a few minor repairs like sanding down and repainting the surface rust on the rockers, i knew when i first bought it there was an exhaust leak. Turns out theres a small hole around the size of a nickel in front of the catalytic, that mount snapped and the chunk it was rusted/fused to came with it. i tried that putty crap and no luck, any advice for a quick fix because i cant replace that whole pipe without doing the manifold because its fused there aswell.

 

You can try cutting a steel soup can down the entire length allowing to to collapse on itself. Cut it into a "C" if you will, then it should roll up like toilet paper. Then take pipe clamps and clamp it down over the hole, so it tightens up. It'll still leak, but if you are talented with a welder you may be able to seal it up a bit.