Gas cap question/pic

One thing to consider is the filler tube. Some of them fastened to the inside of the quarter and some go through the quarter and fasten from the outside.

As for me I don't remember. BUT if that has been removed at some point and put back in the wrong way that could be the problem, or at least part of it.

What car are we working on here???

1976 duster, that makes sense, it was on the outside when I got the car, but it may need to be installed from the trunk side, thanks