Cat back flange leak

I've been searching forever and can't find an answer. I had some exhaust work done yesterday and had the exhaust cutout that I had kept open taken out completely. Now that it's all going through the muffler, I can tell its not the cutout that was leaking, it's the cat back flange. I had ran a few days with the whole exhaust off from that flame back. The guy at the exhaust shop said that I had a gasket leak. I take it off and the gasket is not there. He said it was spring loaded but I have no spring of any kind. I picked up a donut gasket and threw it on but it's still leaking. Any ideas on what I might be missing or might need to do to fix it? I've lost a noticeable amount of power and it has no sound really, just sounds like air blowing. I'm running a borla xr-1 muffler which is supposed to be pretty deep and fairly loud but I'm getting something more quiet than the TRD exhaust, what I'm guessing stock would sound like.

 

Will do, thank ya Chris! You and whipper seem to always be the first to help and are usually right well whipper usually shows up to give me a hard time and tell me I'm a stupid kid then offer advice haha

 

If it still leaks after what Chris mentioned, then take some pictures and post up where the affected areas are. It will help us to better diagnose the problem. Again, only if it still leaks.