There's supposed to be a gasket in there? wtf. I removed my exhaust several times and never saw a gasket. How can you tell if the connection is leaking?
You may not have noticed the gasket as it appears to be part of the cat (I sure didn't, see my post above.) Bascailly if you take the exhaust off, and look at the car, if there is quarter round circular connection there (CONVEX), your looking at the gasket. You have to actually pry/pull it out of the cat to remove it. If all you see is a CONCAVE metal, then no gasket.
Easy ways to check for exhasut leaks:
1) Ear test. Does you car now sound like an early 70's Chevelle or Nova? (you have a bad leak)
2) After the car has sat for a while & exhaust has cooled. Start the car. Look under the car, and see if you see any condensation either dripping from the exhaust connections, or on the ground under the car. If you see water from anyplace but the tailpipes (or if an after market, from drainage holes in the system), then you definatley have a leak.
3) Start the car up from cold, and then spray soapy water on all the exaust connections. You will either see bubles being formed (were exhaust is leaking out), or the soapy water being sucked into the connections (were air is leaking in) if you have a leak. You have to do this a soon as you start the car, as the exhaust will soon become hot enough to just evaporate all water on contact.
Exhaust leaks suck ass. I've found it hard to completely eliminate them on an aftermarket Stainless cat-back with connections, due to the expansion/contraction properties of the stainless steel. If anyone has any sugestions (besides welding), I'm all ears. I'm really sick of leaks.