My mirrors went limp too.  I did the drill-a-hole-insert-pin, and it worked
OK for a while.  Still not firm enough for highway speeds.  My cheap fix was
to set the mirrors exactly where I want them, then I ran a small bead of
epoxy around the ball joint.  They stay in place now, but they aren't
adjustable -- that's OK, I don't let anyone else drive my baby.
That's my dos pesos worth.

Bill Marshall
85 GL Tiico
Phoenix AZ