Rox, I agree, I think a call from MB to the sales manager, would do it, bad press and all that, but for that, you need to get to the senior managers at MB to do it. As glos guy points out, to start all over again would be painful, and like you I would be resentful at paying more, which could spoil the enjoyment of having the car.
Pursuing any complaint of this nature, does require some confidence and energy, which not all of have, best bet is to let motobility deal with it.