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These messages as related to exhaust leaks (which can among other things cause fires) interest me because I haven't YET had any rear exhaust problems. But I almost did.
I consider my aircraft to be pretty well maintained, yet at the last annual the A&P noted something that had essentially been overlooked for perhaps some time. The two holes in the rear cowling where the exhast pipes come out, had small wear marks in the bottom.
The exhaust pipes were well above those marks, so it wasn't like they were rubbing on the bottom of the holes (while on the ground). But if you put a lot of weight on the spinner you could see the engine go down to a point where the pipes were getting close to hitting the bottom of the holes.
So we decided to measure the distance between the bottom of the pipes and the bottom of the holes, and then replace the motor mounts. The net result was that the motor is now raised about 5/8" at static, and the aircraft is much smoother in flight.
Essentially the rubber in the motor mounts had deteriorated to some degree (probably softened) and it allowed the engines to move around a bit (and enough to allow the exhaust pipes to hit the edge of the cowling holes). I can't help but feel that this type of movement and rubbing on the cowling in flight could cause cracks in the exhaust.
So I might recommend that everyone check this by just looking at the exhaust pipe holes in the rear cowling.
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