Recently, the gas cap door on my trusty 2005 Hyundai Tucson popped open and would not stay closed.
It appears that there may have been a small "rubberized" nub that held it closed [my opinion] that may have finally worn down and fallen off.
Does this make sense? Any ideas on how to get that little door to stay closed between fill-ups?

 

If your fuel door release is down by the driver's side seat, they usually have a cable to move that releases the door. If that release cable is sticking in or near the release position , it could prevent the lock from closing fully and allowing the door to open when not required.Suggest you confirm that first.