As I noted earlier, airflow through cowlings can be counter-intuitive. The APS folk put cotton tufts and a camera under the hood of a Bonanza and discovered that, on a serviceable aircraft in the cruise, the air entered the outboard sides of the cowl openings and lots did a lap of the engine bay then exited forward through the inboard sides of those openings.
That data explained why an engine oil leak results in oil on the windscreen- at least on that aircraft and ones with similar cowl airflow ‘dynamics’.
Think about that: air flow both in and out of the same cowl opening. I say ‘opening’ rather than ‘inlet’, the latter of which is the label resulting from the intuitive belief that all air comes in the ‘front’ (the ‘inlets’) of the engine cowling and flows rear wards then exits somewhere different.
When there are cracks in exhaust plumbing and holes in the engine bay that shouldn’t be there, who knows where gasses may be flowing, absent some tuft/camera data to show what’s really happening?
And as I also noted earlier, if you think that the cabin windows/cockpit doors being wide open reduces the risk of potentially hazardous levels of CO in the cabin, my experience (with a reliable CO detector) is the opposite. But it did depend on a number of factors like wind direction/speed. The CO reading went to zero once all the windows/doors were closed and the aircraft was flying. The short term on-ground exposure to CO in a serviceable aircraft was evidently not deleterious. But who knows what could happen with repeated exposure during repeated short duration ops combined with with defects in the engine bay? The science shows that CO is very ‘sticky’ in the bloodstream.
Who knows what happened in this case. At least somebody’s entertaining the possibility that it’s not all the pilot’s fault.