Just bought a 91 LX 5.0. It had a small exhaust leak at passenger header-why? The midpipe was smashed from running over something, or so I thought. Replaced midpipe with MAC offroad. Fixed, NO! Pull off the midpipe and could see that it was not meeting the header collector well/cleanly. So, I bend the collector, add some muffler paste and re-tighten. Fixed? NO! So now I'm mad, pull of the mid-pipe again, (thank god its in three pieces) Clean the mating surfaces and add a bunch of high temp RTV. Fixed? NO! So then I think I'm going to cry but I think maybe I'll check the header mounting bolts (duh!). Fixed, YES! Moral of the story is this when troubleshooting, exhaust (pun) all theories, don't get set on one.