This is the way I repaired mine, but I found that the o-ring abraded away after a while as I had used a soft, plumbing o-ring. I think an oil resistant o-ring made of viton type material would give better results as they are more resilient.I removed the entire mirror assembly to my work bench and gently and terrifyingly popped the ball joint out of the base, inserted a small o-ring (1/4" in diameter-ish) and gently hammered it back together. Nice and snug now.
TBH, I didn't have an o-ring so I cut a 1/16" slice of 1/4" vinyl tubing.This is the way I repaired mine, but I found that the o-ring abraded away after a while as I had used a soft, plumbing o-ring. I think an oil resistant o-ring made of viton type material would give better results as they are more resilient.
Yes, challenging. I put a folded towel down on the bench to protect the mirror, placed the mirror face down as you have in your photo, one hand on the back holding it down. I then grabbed hold of the "stem" and very VERY GENTLY pulled up on the stem with increasing force, "levering" the stem against the side of the socket, until the ball finally popped out. I then took a moment to calm my breathing....How did you manage to pop the ball joint out?! Here are some pictures of the back of mine for comparison. The inner "gasket" of mine appears to have a split in it (upper left of the joint). I thought maybe messing with this would get me somewhere, but I got nothing. Getting the ball out without doing some serious damage seems... challenging?