the small metal disc in the top of the fuel filler tube is stuck in the open position. Is it possible to release it?.

 

iown, I would get your hands on a small tool like an o-ring removal tool that has a small hook on the end. Then you can stick that down the filler neck, grab the end of the flap and pull it closed a little bit. From there you can see what is going on and what may be the next check that needs to be done.

 

It is a spring loaded flap so hopefully it is just stuck....the consequences if you decided not to fix the small metal flap is the flap functions to keep junk and small things out of the fuel tank. If you aspire for perfection and it doesn't spring back into place your looking at a costly filler pipe replacement.