hey
is the lever for the fuel cap bent? the one you pull to release it?
i don't think there is really a fix for a stretched one.. maybe you could find a mk3 one or something similar and see if you can jimmy it in there to work.. replace it.. i would think that a mk3 one would be of similar length and would most likely work identical
what part is troublesome? does it not release when you pull the lever, i would just try and trace the cable right back and see if you can find anything visible that would create this problem
let us know how you get on