Sounds like you need high temp silicone / anti-seize in between the gaskets.

 

Exhaust leaks wont hurt for a long period of time. They do sound like shit though.

I had one on mine when i installed my exhaust system, I just drove it to the shop, picked up high temp copper gasket maker. Waited for car to cool down and poof, insta-gaskett.

 

Get the grim speed 2.5 to 3 inch adaptor. It will fix the issue.

 

i've only seen thsoe in the 3inch DP to 2.5 inch catback, not the other way around. fi they made the other way, a link be appreciated.

 

Just throw the donut back on. The catback will cut into it a bit but it will seal. I drove my car like that for 10,000 miles like that. Just use locknuts and dont tighten the shit out of the bolts and break the flange on the catback.

 

I put the donut back onto it and problem solved no leak. Hope this helps someone some day!

 

I have this same issue with my CNT quad tip. It almost drowns out the leak sound but I'm just waiting to install my downpipe. I suppose the exhaust adapter might work. The way I was looking at it, I don't think it will. I think the adapter goes a little on the inside of the exhaust and there is some sort of metal piece in the stock downpipe right at the end there. I wish I had a picture.