[T2] Tracing "a smell" through air vents?

[haluska john]

Hello,

  I am the on the endless quest to eliminate the noxious smell coming from my air vents when my car is running.  I have had the engine dropped and resealed at many of the leaks and the smell still remains.  I was told that it could be remaining oil in/on the heater boxes that will take some time before it burst off.  It got me thinking: “How easy is it for a novice to swap those out?” and more importantly “How do I know it is coming from there and not a leaky exhaust or muffler?”  I am determined to get to the bottom of this and to correct it (Damn it!).

 Thanks,

    John