When the fuel filler cap failed on my '91 245, I smelled it only when I walked near the fuel filler door outside the car.

As I recall, the fuel neck and vent line are visible from under the interior panel on the passenger side of the cargo area. Check for a crack or failed hose there.

Also, I think that I remember seeing the hatch where the fuel level indicator goes into the fuel tank when I had the floor up putting in the 3rd seat a decade ago. If you don't have a book to confirm, pull up the deck and the metal plate in the floor behind the rear seat and see if my memory is correct on this. Don't be surprised if you find that the sheet metal screws are stripped out in their holes. Most of mine were stripped, so I put in larger screws when I put the plate back. (If that is indicative of the assembly line work, no wonder the car has rattles!)