Welcome to the forum. I don't know your model so I can not offer constructive comment on your speedo issue. It may be cause by PO switching to different wheels/tires. I think calibration may require removal and sending to speedo shop.

__________________
Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html