M50 Exhaust Leak
 

I got new cobra exhausts for my bike and I have an issue installing them. There is an exhaust leak on the left cylinder when I put on the new pipes. I have tried taking the exhaust and re-seating them twice. Are my pipes just bad and I should send them back? Should I be using a gasket of some sort? I'm pretty new at this so please ask for anything I left out.