The gas cap tether on both my 05 and 08 outback broke. getting forgetful and not wanting to leave it at a gas station or on the roof of the car...
I searched around on the web and found someone making a replacement for about $10. Subaru only sells the cap which comes with the tether for about $26.
I saw a youtube video where they lapped the broken ends, glued them and used small zip ties.
I have a simpler solution and time will tell if it is durable.
I didn't use any adhesive but just jammed the broken ends into a small piece of chain saw gas line. I don't know the exact id of the line but it was a real tight fit and seems to be holding. If it fails I might consider some silicone or other adhesive like M-1.
sorry picture attached out of focus.