the requirements for the fuel cap are that it forms an effective seal,not clear from your post whether it does up or doesn’t or whether its got some sort of flap that’s not working etc,any danger of a picture?if youre only bothered about it locking that’s not a requirement as long as its fastening correctly.if in doubt a new cap from a local factors isn’t generally more than a tenner anyway.if youre too skint for that then head into any local fuel station and tell em you left your cap there a couple of weeks ago,they all have boxes containing dozens of homeless fuel caps left behind and will generally hand you said box,go out to your car and you will generally find summat that fits.
