I do not know what kind of an exhaust system you have, but the general issue is the area that needs sealing: Is this a wet exhaust, or a dry exhaust. Then consider this: Does the area that is being sealed heat up or stay "room" temperature.

I replaced the wet exhaust system from the manifold to the plastic muffler with ordinary plumbing parts in Hawaii and made the mistake of using Permatex gasket in a tube as a sealer. After motoring out of the AlaWai Marina thick smoke was coming out of the engine compartment. There was no fire, just the Permatex gasket stuff frying. I got seasick for half a day from the smoke, and I replaced the sealer with Teflon tape in the next port (Nawiliwili/Kauai).