I just replaced the resonator and muffler on my son's 95 Accord Sedan LX with federal emissions. Used Bosal parts for everything. Where the cat converter connects to the resonator is a circular aluminum o-ring type seal. There are three studs on the converter and the o-ring fits into a groove here. I put everything back together, but I can still feel air. How do you get these two mating surfaces to seal?

 

I think on that part you have to tighten it evenly, not fully tighten them one at a time. Tighten one slightly, then tighten the next one slightly, and so on, so that the gasket seats properly

 

You're definitely right about that part. I did that by tightening a turn or so on each nut. Granted, I was doing this with the car up on ramps and a jack stand on one side for safety with me lying on a piece of 1/4" plywood on a gravel driveway. The ring is like a compressible piece of aluminium which slides over itself when compressed. It did not fit exactly in the hole as I expected. I probably pinched it somewhere where I couldn't see it. Oh well, back to the drawing board.

 

You can use exhaust paste to help make a seal.