83 SN Exhaust Leak?

With the engine cold you can feel around the manifold with your hand for the leak for a good 2-3 min before it gets too hot. On a warm engine you can use a 3' to 6' legnth of 3/8" hose like a stethascope. One end to your ear and the other to the noise. Move it around the engine until you find the culprit.    

I use usually automotive exhaust manifold gaskets (Block to exh man) since it is the same exhaust and not exposed to water. Most parts houses can match up your existing manifold gasket.

It is also suggested that you file the mainfold mating surfaces smooth and flat when you regasket. Some marine castings are not flat and true when new. I also like to replace the riser gaskets too ~ But they are boat store only and usually require preplanning / order in advance and delay for shipping.

As for the spray ~ that is usually reseved for finding vacuum leaks on the intake side.