Logic? Okay. I’ll explain it all out. Slowly. The rotten egg smell comes from an excess of unburnt fuel. Combustion, all of it, produces CO. If you can smell the unburnt fuel in the car, there are exhaust gasses in the cabin. Back to the fact that all combustion products CO, and you can smell excess unburnt fuel in the cabin ........ there WILL be CO in the cabin as well. As for your snarky comments on the exhausts, there have been reports of CRACKED manifolds. A brand new, entirely unrusted manifold can crack. And, of course, Ford Has had manifolds crack and fail before.