Yours was the original post I found to get this project going; thanks!
As you prolly know, the mirror is a bit odd. 2(or maybe three, but I cannot feel the last bolt) bolts secure the mirror to the Coach A Pillar. Subsequent to my last post if I lay on my back and reach up, under and into the dash, I can just feel the (2) bolts heads; they are tight.
The mirror...pedestal, for lack of a better term, then has the black plastic mirror housing bolted to it with those wonky inserts. The bolts go through a flange on the outside end of the pedestal, and screw into an inner thread on those wonky steel inserts which were screwed into the plastic. With it all covered by the rubber.
Basically, this whole shebang is based upon the mirror never being placed in tension - cause when that happens, the inserts strip out of the plastic and your mirror goes all jiggely. This could be caused by hitting something, a bird strike, maybe a rock, and maybe even too much wind speed over time.
Guess I should not complain too much, as it lasted 20 years. But every one of these mirrors will eventually fail in the same manner. Unless the motor burns out first. But that said, I stand by my earlier comment - it is a crap design. Stressed members and plastic rarely include longevity as a byproduct.
Not to digress.. well, it's my thread, so I guess I can:
A few years ago I had reason to be in the Ford dealership in Silver City, IIRC. Friendly folks, and they let me wait to speak to a mechanic in the shop while he was working on some high performance Mustangs. He had (3) Mustangs he was working on, all with the hoods open, and doing the same job on each: replacing the PLASTIC intake manifolds. This is a big job, if you have not seen the engine bay on a hi-po Mustang lately. Seems Ford misjudged how much plastic to reinforce the heater hose connection with, and they were all cracked; same place, every one. All being fixed under warranty. I asked to see how the new one was made, and he pulled one out of the box for me. The new part had a metal corner cast into the plastic manifold. The engineer on that manifold screwed up: it did not make it past the warranty period...
If it had, all those owners would have been SOL...