Actually, I think the problem you've described may not be an issue at all. Were you aware that the fuel filler door locks when the car is locked? What may be happening is that when you get out of your car at a gas (petrol) station, your passenger door remains locked. Well, when the passenger door is locked, the fuel filler door is locked as well. Given this design feature of the car, I have learned to press the unlock button on the door prior to getting out to fill up the car with gas. I discovered early on when I got my car that this was why my fuel filler door would not release.