Exhaust dilema

My 93 Caprice Classic Police package 9C1 single exhaust needed to have everything from the convertor back replaced. Two years ago the flange that held the intermediate pipe to the convertor had rusted off and it was replaced with a split flange, The split flange had warped and so when we dropped the old exhaust we noted that the round mating surface on the end of the convertor was slightly distorted as well. Possibly from the unequal pressure of the deformed flange, but I don't know. We straightened the convertor end as best as we could with channel locks and assembled the new parts. We used a correct new intermediate pipe with a stock flange, the correct exhaust pipe, an aftermarket muffler and we eliminated the resonator and replaced it with a straight piece of tail pipe. Now there are some problems. First, the flange did not seal properly and it leaks. I was told by a guy a Meineke that they can "rebuild" the convertor end when this happens for 49.00. Someone else told me that I should take it apart and put muffler cement on the mating surfaces and then put it back together again. I am willing to try this but truthfully I have my doubts as to how effective or permanent this might be. Has anyone had any experience in using this stuff in this particular application? My other problem concerns me more though. Both the cat as well as the muffler seem to be running much hotter than they should. I also have noted that my RPMS at idle are lower as is my oil pressure at idle, and the engine seems to be running a just a bit hotter too. Now this aftermarket muffler which the book says is the replacement for this car, was three inches shorter and it was shorter in width than the original as well. In fact the installation required that we install a small extension pipe on the end of the muffler to make everything fit. The parts guy says this is no problem as often times aftermarket stuff is made differently but has the same specs. But I'm wondering about back pressure now and I have no way to confirm if it may be incorrect. And if it is would this likely cause the problems I'm having? I would really appreciate any and all thoughts and comments on all this. I'm getting so tired of lying in the dirt on my back. I'd just like to see this resolved correctly once and for all. Thanks very much. Lenny Stein.

All very common stuff. I had all these troubles on my '91 9C1. That pressure-flange GM uses on the outlet of the catcon is OK for the warranty period...then it just doesn't do so well.

Pfft. No. It will leak again. Replace the converter. (At one point, when a friend of mine owned a '91 9C1 very much like mine and lived in a location in the US where there has never been (and will never be) any kind of auto inspection, he took a careful look at the converter catalogue at the local NAPA, ran over to a custom exhaust place, and said "I'm putting in a stationary generator set and to complete the exhaust pipework, I need a straight piece of pipe such-and-such inches long, 3" IID at one end and with a 2 1/4" inward-rolled ball flange at the other". Also need the flange plates." $30 later he was outta there. Of course this is illegal and etc.)

Yeah, right.

Muffler cement: If it seals, you didn't need it. If you need it, it won't seal. Don't waste your time or money.

The L05 engine is a dirty runner and the converter is very far away from it -- both conditions tend to stress the catalyst. These cars, therefore, are tough on catalysts. It's a good bet yours is partially clogged or melted.

Bzzzt! Cheap economy "Pro-Fit" muffler. NOT the correct item! Donno which "book" you were in, but you got steered wrong.

Horseshit. The correct muffler can be had at most any parts store -- you just have to insist on an OEM-quality, direct-fit muffler. All the major aftermarket exhaust companies make it.