Finally found how the exhaust fumes were leaking into the car

Harley guys? When we lived in north-central Pennsylvania (small rural town), there was a local guy who rode his Harley all winter long, assuming he rode to work, because I would see him about every day. He had what looked like the frame for a side car attached to it, and a large car battery strapped to the outside end of the outrigger. Rain, sleet or snow never stopped him.

Glad you got your exhaust problem fixed.