Mine seems to get worst after warm up. Yes, I suspect it might be a crack inside the heat exchanger (its GHL with heat) since I can't see any cracks on the outside; and I do smell exhaust in the passenger compartment.
But, how does it explain the fog up on 1 side? Could it be crack only on the driver side HE box hence part of the exhaust from the header is actually sent to the windshield, hence lots of hot air on 1 side?
87 930 K27HFS/B&B/Twin-Plug... Megasquirted