Hi Tosher
I gave the black plastic ball and alloy housing to an engineer freind of mine and asked him how I should fit on to the other. Whilst we were talking he had fitted it by hand! I didnt notice he was manipulating it whilst we were talking. I asked him to show me what he did, and he just offered the ball into the back of the housing, it will only go one way, with the two cut outs. Push it well in with your thumbs, a bit of fairy liquid on the o ring will help, then manipulate the ball around in the housing. It has to be "lined up" quite accurately, but it will go. Magic. No big hammers, no vices. It works, try it.
Regards Coll