I have the “dealer option” Racing mirrors on my 240Z. The ball joint on the 44 year old driver side mirror body was getting loose and would not hold position while driving. It finally got so loose I was worried it might fall off if I hit a pot-hole.
I removed the mirror, and discovered the hole in the mirror body had worn / enlarged to the point that I could easily pull the ball out of the mirror body! I tried a few “easy” fixes, but none really worked, and decided a better solution was required.
So I fabricated a plate that fits over the posts inside the mirror, having a central hole smaller than the ball joint diameter. To get it over the ball, I cut one side of the center hole so I could twist / bend the plate to install it after inserting the ball into the mirror.
My thinking was that the holes in the plate that go onto the posts prevents the plate from deforming / spreading, so the ball joint hole won’t enlarge.
I assembled a “rough” prototype from 1/16” galvanized sheet-steel and it works great! Mirror body is nice and tight with no movement when jarred. The hole in the plate may deform a little over time, but it can only deform so far. If required, tightening the ball joint screws in a month or so should create a truly permanent fix.
Let me know what you think!