For whatever reasons that yoke has been exerting wear on that output shaft and visa-versa for a long time. If you look at the shaft splines you can see the spline profile has been worn on both sides of the spline teeth eventually leaving only a shortened triangle in the place that originally was a splined tooth wide enough that a flat once existed at its outermost OD. That flat is missing and the shaft splines are now peaked, thinner and shorter.