Is there any up and down slop in the top (or bottom) shaft bearing support? With the can and the steering wheel bolted tight, can you tip the wheel up and down? Has the column been bent or partly clasped at some point? As it turns, does the wide part of the gap move around the column?

If the can and splines are good, that leaves: loose screws in the column, bad upper or lower bearings or bushings, a bent housing, a bent shaft, or a bent can.