I wonder about your balance job. If it is indeed that well balanced
you should not be having stuff shake loose. Likewise, with all the shaky
B16, B18, B20 and B30 engines I have owned over the past 35 years I have
NEVER had a solenoid shake loose from a starter, and I've had some pretty
bad starters. Likewise alternators are normally fairly trouble-free.
(That is one reason they are preferred by some to generators.)

Maybe you need to do like the Army motor pool and pull maintenance including
making sure that everything is good and tight.

Do you have electrical equipment that draws undue amounts of current for
protracted periods, or maybe some unidentified short somewhere that is doing
the same thing? Normal electrical load in those cars is the ignition system
in summer at less than 5 amps, or if raining maybe the wipers, at another 5.
In the winter the heater might draw more than that and the lights will also,
but even so, the generators in mine have always been sufficient until the
field windings came apart and the armature tore them up. (I have since found
several rolls of fiberglas electrical tape that does a great job of wrapping
them up, a lot better than the original cotton/linen tape used by Bosch.)
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma