Petrol cap

Help trying to obtain seal for petrol cap 1987 cabriolet not the one for the neck but the cap itself seem it’s a mot failure 

I don't think you can buy just the rubber seal so either buy some rubber and make your own seal or buy a new fuel cap, if you have a GTi then this is the fuel cap you need (not vented) carb cars need a vented fuel cap.

https://www.ebay.co.uk/itm/191428380671?hash=item2c920547ff:g:CVAAAOSwrfhjDxEi&amdata=enc%3AAQAHAAAAsFdIyFklXwX5%2FqUlptsGRS4nbLm8zhOb7SUrxfNPuDc93wB6%2BG0uO4n4HGm5wDpeG%2BNCzXPBcQSScaZnI6wDkWoqXqBDI3xVd%2FoGR5KFXIceJAkZQkGc1Fe82h9fD0wYjh7OY3qGjbMEcfG5U4KO3wHDHBIHqjTHyjsgWo5KI5lzYRe%2BMWrdA74slhcAaHn7qUQ1rKEU1LoOHs8ZjfP7vXCKift25FkC%2F%2FW4%2BegOCFZc%7Ctkp%3ABk9SR-T3kdTQYQ