OK,,, this is from an old mechanic.. ( me ) not an MB person...
One way a vibration could exist has to do with the way the vibration damper is made... with rubber...
I once had an engine where the outer part had rotated from the correct position... due to age/vibration....
and the stupid timing marks were ON that part of the damper...that one took me a while to figure out...
but back to the point here... if the rubber has deteriorated... then it could be ' wobbly' at low rpms..... but solid when thrown outward by centrifugal force at higher rpms...
Just a thought...
Since your vibration damper may be the same age as your engine I think with all the work you have invested to make this about the perfect car it might make sense to just but a new vibration damper on your car...
But I still suggest you check the tech bulletins first....