The ball is diecast. Nylon would never adhere to the motor shaft. One of the problems of the Liondrive system is both the ball and the coupling it drives are diecast. Both are subject to wear if not constantly lubricated. Few do.
Its a poor design given the ball is not easily replaced. I will not buy any Liondrive engines not only for this reason but they also ride higher than the previous worm-worm gear drives.
Pete