rummelpa, welcome to the forums. I am sure you will find us very friendly and willing to help. So, search around the forums and you will probably learn tons about your car and some of its hidden features. We also ask that you stop by the "New Member" section and tell us a little bit about yourself. We are a friendly bunch and you will find that this is really beneficial as you learn who the movers and shakers are around here.

As for your problem. Unfortunately, the only "fix" is to remove the filler tube and replace with a new one. It will unbolt from the car and then you also need to remove the end of the tube from the rubber filler hose. Accessing just the flap is going to be difficult as there is no side access that I am aware of. Everything has to be done through one of the two ends. The flap is assembled before the pieces of the fill tube are put together. It isn't meant to be repaired.