It's important to remember that the first generation Z cars were not designed or built anywhere near today's standards. The Lexus ball bearing test simply wouldn't work. The early cars were, let's face it, built to a price. No undercoating,an unpainted transmission tunnel, very little seam sealer, no screen between the deck lid and the trim panel. That was just the understood industry standard when it came to fit and finish.
As all of us who own a first generation car know; exhaust fumes in the cabin ranks right up there with steering wheel shake above 50 MPH. We'll experience it at least once and go to a lot of trouble chasing it down. Once again a design, fit and finish issue which gets to the meat of this ramble. The factory should have installed a screen between the inside of the deck lid and the trim panel, but didn't. You have, or should have, one on each door why not on the deck lid? After all, that's the area where most if not all of the exhaust fume problems originate. What's a screen? It's a sheet of plastic shower stall liner type material attached to the inside of the doors (between the door and the door panel) with 3M Strip Caulk. If you're pulling out your hair trying to find the source of that stink give this retrofit a try.
Mike McGinnis
Banzai Motorworks