I think the tranny mount will do the trick. Also how long ago did you replace motor mounts? It pays to retorque em after a year or two. Among Vintage MB's the owners manuals listed a bunch of nuts'n bolts that require tightening each 25k miles or so. On this list were motor mounts, steering gearbox mounting bolts, subframe bushings and a few others that i forget. This refers to 111's, 114's but the logic would be the same.