If the dog Fight exhaust uses a manifold that the actual chambers slip onto (and that part has an O-ring where the manifold/chamber slip together) then you want to have some form of seal between the manifold and the cylinder/exhaust port. The stock cylinders do not have a smooth surface for matting a manifold to, so you need either the big cooper crush washer/fitting or some other form of seal (never seen any other seal system for this).

Without a seal, you will get leaks from that attachment point.