Stan, the charcoal can used to sit under the battery tray, front left of the engine compartment. Surely realoem will show you this (I have not looked). By now the cans are rotted and gone, and the vapor hose led to the air cleaner or outside air.
Sven, there are more than a dozen ways for gas fumes to get into the passenger compartment. The tech articles have some listing (or used to on Art's site). Some highlight areas...
The gutter in front of the windshield has three tubular drains into the engine area, which were fitted with rubber tubes. Thise tubes are likely long since rotted and gone, and vapors from the engine come into the passenger compartment that way, among others. CNPR sells reproductions.
You must ensure your trunklid gasket is snug fitting. Again, CNPR sells 6er trunk lid gaskets that are said to be quite tight fitting.
Fill the gas tank, remove the right side plywood cover over it from the trunk. Strongly rock the car back and forth so the gas swishes around in the tank, while observing the fuel gage sender area. There is a large o-ring there that may be leaking gas into the trunk.
The gas line fits over a metal tube on the sender apparattus. They are different sizes, so BMW put a small plastic sleeve over the metal. When owners change the gas hose, frequently the plastic sleeve is discarded with the old hose, while it should be retrieved and reinstalled.
There are many many more ways...
