The next piece of the puzzle arrived yesterday and was installed today:

A passthrough USB plug (under that cap) in case I ever want to plug something in.
I also replaced the TCS button as the clips holding it in were broken.



And for a bonus, I've had a replacement drain tube for the RVC sitting on my desk for months which I put in today too. This is what an old one looks like, note the little rubber end had perished so it wasn't poking out the bottom anymore so would have been draining into the boot lid. There doesn't appear to be any ill effects, although that pipe doesn't look quite so clean and clear as the new one