This is a new MB bolt. The fact that this came directly from MB is what has led to my confusion. Part of what of I'm trying to figure out is whether there are two varieties of bolt MB used for this, and this part number is for the alternate style. There is evidence suggesting this is the case, which would mean the hex head bolt should be an adequate substitute. But no one has yet emerged with a definitive verdict on the two-styles theory. See one of my earlier posts for how we got here.