i just got a new exhaust and the piping is 70mm but i still have a stock cat. the gasket that came with the exhaust didn't fit between the stock cat and midpipe.

what should i do? i have no gasket there right now and i think its leaking a little. Can i use those hi temp gasket makers/sealants like permatex?

 

That will work temporarily, but it will probably blow out over time. Look on atpturbo.com, they sell a lot of different exhaust gaskets.