gidpor, not knowing what homework you did, I was wondering if you have any credible mercedes shops in the area? Perhaps this was one? Did he give you back your old transmission? I would have thought he would have...My only concern is that the new one has no proven history on it. Did he have any records on it or did you go simply by word of "his" mouth? How well did you know this guy? Just curious.
ps: I know these guys can't catch every post but it's too bad 2 weeks went buy until you got a good answer from a credible tech..