HELP! HELP! EXHAUST FUMES IN CABIN

We own a 1996 VW Passat TDI (diesel). We bought the car new. After a couple months, we noticed that opening a window, even a crack, or the sunroof caused exhaust vapors in the cabin. We have repeatedly checked every possible leak including the trunk seals. Someone, somewhere must have a clue of a similar problem in a VW or othef make of car. The dealer put a mechanic and me in the car, raised the car on a hoist, started it to idle, and declared there's no fumes. I told them it's not the same thing as what happens going 30mph, or 70mph. We have tried everything possible for leaks. Tried everything but incantations.

I wrote a very firm, but polite letter to VW of America. Forget it!
I was underwhelmed by their response. They had a young bimbo call me with a series of questions. She did'nt know what an intake manifold was and other car words. I finally said "You don't know anything about cars, do you? She said "I'm sorry" or words to that effect.

NO MATTER HOW FAR OUT YOUR IDEAS ABOUT OUR EXHAUST PROBLEM
ARE, PLEASE SEND THEM ALONG.


PS The car is quite new looking for being a '96 with 250,000 miles on it.
Still no motor work and does not burn oil.
Still gets 45mpg. Overall, an excellent car, except for those fumes.
I won't be getting rid of it, so, I might still get to use sunroof.