I had the same problem with my 71 Non-remote Cuda mirror, no way to get to the ball without removing the glass....Which I didn't want to chance breaking
What I did was remove the mirror from the door, and do a drop at a time of superglue into the ball, propping the mirror upside down, let the single drop dry for about an hour, then rotate the mirror head breaking the seal of the superglue, repeat this a few times until you build up enough superglue to make the mirror stiff once again,,,don't overdo too much superglue at one time, otherwise it gets really tough to break the grip it has...DAMHIK