Funnily enough MK, I do think that you have grounds for a claim too. It's just that putting it to the people in charge in the right way often yields better results - if you know what criteria the MB "paperwork" needs to get a yes stamp, you have a better chance of putting your case in such a way to hit those targets. This is where my comments about building and maintaining a relationship and history with the dealers comes in. The "Oh, this is disappointing, I had expected better of a Mercedes" carries a bit more gravitas too
The tailgate should be a yes, given the location, and I think you would be hard done by if refused on that. Getting an agreement to that might also aid in pushing for the arches too, perhaps with the view that if the bootlid is going unaided, what chance did the arches have?
Remember, work the system, don't fight it