There is no real easy way to fix that exhaust leak.
1) if you have safety inspections in your state, the JBweld will not pass...and it probably is messing with the O2 sensor as well...
2) and considering that the only way to fix the remaining leak is to remove the exhause header, it's best to fix it the right way..
Here is the problem...Cherokees have a real bad problem about exhaust manifold cracks..check out
http://www.nhtsa.dot.gov/ for any recalls on your jeep for exhaust cracks.
They had several voluntary recalls (meaning that the dealer can call you if they really feel like it)
Most likely, the existing leak is the exhause gasket on the last cylinder...this happens alot. In fact, it just happened to my '89 Wagoneer LTD...I had to replace the gasket...not a job for the weak or the unskilled!
To get the exhaust manifold, you have to remove the power steering pump, (put it out of the way) remove the fuel injection rail, disconnect everything connected to the intake manifold, remove the EGR tube on the exhaust manifold, disconnect the exhaust pipe, then unbolt all the bolts holding the intake and exhaust manifolds on...you see, they have to be removed as a unit! a royal pain! I found that the last bolt in the very back against the firewall almost impossible to remove...Once you get the intake an exhaust manifolds off, take the exhaust manifold to a machine shop and check that it is still true...sometimes they warp due to the heat. If it is still true, have them weld the broken seam. Then pick up a new gasket and the installation is the reverse of the removal (don't you hate it when the books say that? Installation is NEVER th reverse! It's always more difficult!)
One trick before you get everything bolted up! that EGR pipe? When you get the intake and exhaust put on the engine, and BEFORE you put on any of the bolts, connect this pipe first...you will never get it connected if you don't!
Well, I hope this gives you a little insite on what you will be needing to do!
On the flip side...my mechanic charges $500 to do what I just described...some charge more, so use my number as a reference only!
Ed
web/gadget guru