I'd appreciate knowledgeable input on this issue, and not just a knee jerk reaction "carbon monoxide!!!"

Rotax 912S, which uses a stainless muffler and partial shroud over it for cabin heat. SCAT tube leads from the diverter to the cowl nostril for intake. The diverter either shoots the exit air from the cowl out the bottom of the cowl, or into the cabin. With nearly 3 K hours on my S-7S, I am looking at my third, maybe 4 th diverter, and that's only with major patch done along the way, and they still always leak a little hot air in the summer. It's a pain to get at it, and since the intake is readily visible and handy to get at at the nostril, I thought of fabricating a shut off flapper right at the front, using a micro linear actuator and a remote control for it, (readily available, light, and they work great, have one on my oil cooler shutter) and doing away with the diverter entirely, controlling the needed cabin heat by adjusting a simple flapper valve right at the SCAT intake.

Question: is it required to ALWAYS have air going thru the shroud, like the current diverter does, and if so.....has someone else trying this approach actually had a stainless muffler overheat or burnout due to a blocked shroud intake? I fully realize the serious of fooling with the exhaust system, but now that I think of it, past summers have found me using duct tape to close off the cabin duct exit due to a crappy diverter letting hot air in the cabin so I guess I have already tested the concept without any ill effects on the muffler. Maybe the temp difference of a blocked intake isn't enough to matter on the stainless?

I asked the same question a while back for similar reasons and was told to keep air flowing. So until I fixed the diverter I blocked the majority of the shroud inlet but not 100% (it was summer and no need for cabin heat). You could probably just modify your current napkin design with a hole in the plate large enough to keep some air flowing through the shroud but not enough for a meaningful cabin leak?

I’m curious to see if what I was told holds up to the consensus over here, too. Your idea might be a better solution for the 21st century if the shrouds don’t need constant cooling airflow.

EDIT: fixed a typo

I pretty much got talked out of the concept after talking with Clint at Vetterman Exhaust, and Charlie at Aircraft Exhaust Systems, both were very helpful. Loss of ambient/unobstructed air by a totally blocked shroud intake not a good idea, Clint quoted numbers at me about different types of stainless and what happens when a certain high temp is reached, So, a good idea that was also a bad idea.
What the world really needs is a better quality, longer lasting diverter, and maybe easily rebuildable to boot.