Just went for a ride, twice a cloud of exhaust came thru my defrost vent on passengers side. I have not had this car long but have drove it a few times and never saw this before.

I had that on my first 914. Rusty heat exchangers will let oil leak down (due to dripping from a leaky valve cover) onto the boxes, then past them onto the pipes.

Stopping the leaks, then cleaning your exchangers really well will help.

Oh, I had the car up on jack stands all day (rear end up), then I spayed the bottom of the motor/tranny with carb cleaner, wonder if that had something to do with it. I just drove it again and no problems.