W126 suddenly has gas smell inside passenger compartment and trunk after last fill up

[86560SEL]

My old (now my moms) '88 W126 suddenly started smelling like gasoline on the interior a few days after the last fill-up a couple of weeks ago. I took it and filled the tank (we try to keep it filled up since the gauge is inaccurate even after spending $700 to get it repaired a couple of years ago).

Anyway, the car didn't smell like gas that day... it wasn't until about 3 days later when I went to get something out of it that the interior reeked of raw gasoline fumes... as well as the trunk. There are no leaks anywhere.

I always top it off (which I shouldn't and will not again). I thought maybe something was wrong with the seal on the cap, so I removed it and gasoline started GUSHING out of the filler hole. The car was setting with the right rear being the lowest point however, so I guess that is normal, lol. There was no gasoline seeping out of the cap however.

I didn't get to look at the seal due to the gas pouring out, so I had to put the cap back on posthaste. Does this sound like a bad gas cap seal causing the odor inside the car, or does it sound like something else? Is there a trouble spot on these cars that allows fumes to enter the passenger compartment, but with no visible leaks? I am hoping it is as simple as needing a new cap.

Thanks!