"Well I'm happy to suggest that a properly-maintained aircraft is very unlikely to expose its pilot and passenger(s) to excessive carbon monoxide."
Agreed. But CO accidents are very infrequent.
What maintenance check detects a thin spot in an exhaust or a developing gasket fault?
I've had a few exhaust replacements and exhaust gasket leaks, but ALL were spotted AFTER the leakage had started, sometimes with detection in flight by engine noise or CO detector - spot black and detector (from B&Q) bleeping. Sometimes at check by soot stain.
But the leak was already there.