...thanks for the posts guys, add me to the list, putting gas in today and the door was just flapping away. First thing I did was a search here. I see the pin has broke. I think I'll try the velco or magnet, since a new one is likely to break in short order.

 

I have had this problem twice and fixed it myself both time. With the last time being yesterday. For you all that may want to do this your self and not have to keep replacing this. Here is what I did. Inside the gas cap by the tank nozzle, there are 3 screws. With a socket wrench you remove those screws. Once those are out you remove the yellow plastic piece around the nozzle. It just pops on and off. Then with a flat head screw driver you slide it in on the right side of the nozzle cap where the door latches and slowly pry it away so that it is at an angle. it will then totally pop out.

After you have it out you will see where there is a pin and spring, the pin slides itself out of the whole as you keep opening and closing the gas cap door. The permenant fix to this is to slide the pin back into the hole and when it is fully seated take a hot screw driver tip or soldering iron and flare the end of that tip just enough so it won't be able to work its way back. Did that to mine and it has never come apart since.