I read that, but how far do they move? I figured you meant slightly, which could be from vibration and looseness of the inner mirror section. They are very reliable, seeing how good they work after 20 years. If one has issues, I'd not fight it, and replace it.
I'm fighting with the rear hatch of my new 98 recently, the right striker keeps breaking apart. I'm fairly sure the past owner caused damage to the hinge from an antenna mounted at the top right. The hatch did fine for many months, and then the original bushing cracked and I replaced both sides. Now the right one has broken three of the parts store replacements. So I've swapped an original one from my Mercury, since it's been perfect always. I bought new hinges, and though the two on the truck appear okay, I think at least the right one is worn, and letting the hatch move too much.
At this age of our vehicles, maintenance is really important, and replacing old parts that never get a thought, is also big.