I'd also love to see how anyone modded a cap. I found it difficult to get a spare cap, seemed everyone on the bay knew how much new ones were and only knocked off a quid or two making it still expensive. However, I do have a spare since I had to change the brake master cylinder thing is I've cleaned up the garage and for the life of me I can't find it. Will have a look tomorrow and drop you a line if it comes to light.