Not exhaust gas but hot air. On my '84 BBi the console must not be sealed because with the windows cracked or down, you can feel hot air coming out of the shifter area, and defrost lever bezzels. The airflow around the cabin also sucks in hot radiator air which seems to flow up over the windshield, and into the open windows. Apparently there is a vacuum created in the interior with the windows down, and air is sucked out of the interior somewhere. If you smell exhaust gas GET IT FIXED. There are numerous gaskets in the exhaust system on the car (I know, I've replaced them all) and plenty of room for leaks! Don't let this go unattended.