Most interesting. I didn't know that. Very strange. The Monroney label on an M50 shows the Calipers as part of the MSport Package, although the MSport Package is (I think), a standard package on the M50. FWIW, it seems that one can do a DIY MBrake upgrade to an i4 40 using BMW P/N 34108854026. Although this Part Number is active in the BMW System, it presently does not allow a dealer to order it. Some on-line dealer websites show BMW P/N 34112450161 as an active number as "M Performance 18” red sport brake retrofit kit" but at $2,495.00 I'm not real anxious to experiment.