Exhaust smell through heater
I've been fighting with a bad exhaust smell on my '83. The muffler needed re-welding and a tune-up helped a bit. However, I still get bad fumes when I run the heater. If I have the heat slider turned to cold it doesn't smell much. But when I have it set to hot, it smells in the cabin.
What should I be looking for and how should I track it down?