Mr. Wolz,

Every mirror I have had has slipped and moved at one time or another,
and been impossible to permanentley lock down  tight, prior to the stud
flying out of the mirror arm.
It made me cranky.
I got tired of removing the mirror's and making this adjustment.
I got tired of the frozen nuts snapping.
I got real tired of the studs pulling out.
If in the 600k miles you driven you would exceed the speed limit you to
may have been exasperated a bit more with this never ending problem.
I cured mine, with a simple visit to the archives, and through the
process of elimiation of solutions.