It seems they all crack. People have reported pulling a NOS steering wheel out of a box and finding the same cracks as we see here. The plastic coating must simply shrink & deteriorate over time and it gives out.

Another point about seeing it if "spins straight". Many of these steering wheels are NOT truly round...they are slightly oval shaped...wider than they are tall. Some have reported straightening the oval in a press prior to a resto, but I do not believe this to be a correct process...