I do not remember the setup on manual shift Benzs but most engines require a pilot bearing inserted in the end of the crankshaft to center the input shaft of the trans. With an automatic you have the hub of the torque converter in the same hole. No where in your posts did I notice the mentioning of a pilot bearing. Did you put one in? If it is not there the input shaft will not be held in proper alignment and will cause a vibration. It will also lead to premature input shaft bearing failure. HTH.

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