Thanks to Tanasit for the following text and pictures :

One day I was flying in my living room and landed the tail on a pile of vhs tapes.  I heard a loud crack but thought it was just the tail blades hitting the plastic case of the tape.  Upon closer inspection, the ball on the tail blade grip broke.  I epoxied it first but no use. And since I don't have any spare, I came up (over night) with the idea of putting on the metal ball in place of the broken plastic one(s).  I found some metal balls from my Concept EP spare box and some self tapping screws which are about the right width and length. I filed off the stock plastic ball stem and drill a small pilot hole (at the angle where the old ball was by comparing with the unbroken one) all the way in and a larger one half way in, then I screwed the metal ball with the self tapping screw.  This works great with very smooth and slop free action.