1995 Subaru Impreza

I really hope that there is someone out there who can help me with this. I have a gas leak in my gas filler tube and I do not know how to go about correcting this problem since this is not something that they sell at your local auto parts store. Can anyone shed some light on how I can fix this problem? I hope there is something I can do because the car runs very well and I love it.

Thank you!!!!!