I just got off the phone with the MB service centre and they were adamant that it was classic case of uneven wear on tyres. I told them that you had refitted new wheels and tyres and yet the problem persisted.
There was silence over the phone ... and then "maybe its a strut or somewhere along the suspension BUT I still think its the tyres ... ".
Hmm ... I do hope we find a cure soon as its affecting me too ...