Borrowed your photo... I had a 1956 Chevy and the down side of this was that sloppy attendants would get gas all over the tail lights, and as cars got older and seals shrunk gas would wind up inside the lenses. I had my car in the late 1970s and had to replace both lenses because the fuel over the years had ruined them. I believe these had cork gaskets on them too,
I also remember those fillers behind the license plates... and how the spring holding the plate in place would eventually break. How many cars did we see on the road with these broken and the plates hanging down backwards?
My only problem today is remembering which side my filler is on when I drive my different cars. Both my Caravan and Breeze have left side fillers and my Jaguar and Geo Tracker have right side fillers (cars designed in RHD countries)!