Just in case it can help anyone else, I've just had to source a new petrol cap for my 1995 940 2.3 SE LPT Estate. The below item from Euro Car Parts is a perfect fit and comes with two keys...
https://www.eurocarparts.com/search/334660110
Euro Car Parts also seem to have a never ending range of discount codes available, I only paid £22 for mine, not the advertised price. A lot of used items on ebay etc were the same price.
Car is still going very nicely, picture (hopefully) attached...