[Bertiebloke]

I can give you my simple two step approach to getting the fuel flap to stay closed

1. Spend 3 (or more) frustrating hours trying to get the spring attached. A pro once told me this could be a days work
2. Give up, go indoors and get a few small, thin strong magnets, position them on inside of fuel flap. Adjust magnet position so flap positively clicks closed but is not so strong that you can't actually open it. It has worked a treat ever since.