Charlie,

I suspected that you would have this problem.  The stud that the spring and 
nut fit is a press fit into the mirror housing.  What happens is that the 
stud pulls out a bit, and the mirror loosens.  After a few rounds of this 
the stud finally pulls all the way out and the problem becomes evident.

My solution was to drill all the way through the housing and insert a bolt. 
 I countersunk the head and it looks like it came from the factory that 
way.  My fix has now lasted longer than the original stud.  Both mirrors 
failed about a year apart in about 1990 for my 1984.

I believe others on the list have threaded the hole and replaced the press 
fit stud with a threaded one.  I don't remember anyone trying setting the 
stud in epoxy, though that might work too.

In any case, the fix is a whole lot easier than electric mirrors and is 
permanent.

Mike