SD--The list of things that are "not" on the boat is much longer than the list of things that should be on the boat.
I was being sarcastic about the headaches. On the rare occaision that we motor for a few minutes to anchor, moor or pull into our slip, the the companion way is open and well ventilated. Obviously that is not a solution to the problem. Your CO2 suggestion is appreciated and I will add it to my list of things to do. However my spouse seems to be an effective detector.
By replacing the exhaust elbow, hoses and clamps hopefully I will be temporarily lower my risk of inhaling toxic fumes.