Dear jwalker,

Hope you're well and stay so. To leverage your idea, before start-up, wrap clean, damp rags snugly around each exhaust manifold arm, where it meets the head.

Damp rags won't burn. Damp rags are more easily compressed and so more likely to form a tight seal.

Start the engine and listen for a moment. If there's no noise, that suggests one of the gaskets has failed.

Then, remove each of the rags and listen for a moment. When the noise is heard, that points to the failed gasket. At once turn-off the engine.

It should be possible to finish this test before the manifold is so hot, that touching it will cause a burn. When doing this test, there's no reason not to wear gloves: sound - not touch - conveys the test results.

Hope this helps.

Yours faithfully,

Spook