I've checked all the previous threads relating to replacing power aerial masts on a VX, but none have covered this one...

I've unbolted the aerial from the car and taken the old broken aerial mast out of the metal sleeve. However, I can't get the new mast in to the metal sleeve. The new mast is exactly the same as the old one. There is a black plastic ball at the tip of the mast, and a white plastic sleeve at the bottom of the mast. Neither will fit through the narrow part of the metal sleeve.

Can anyone help?