A thought triggered by the cabin-vent-flap post: What happens on AC when you hit the recirc button?
I'm still looking at exhaust as the most likely culprit, given the known characteristics of CO. Have had a coolant leak into the heater core, and in that particular case there was not only a noticeable odor, but a film developing on the inside glass ('99 Saab in a Michigan winter).

__________________
Craig Bethune

'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)


SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)