Just to follow up on my '84 Wolfsburg Westy with the anemic alternator ...

I bought an alternator at an AutoZone in Flagstaff, just so I would
get completely stuck over the holiday weekend.  I left it in the box,
and in the end I didn't have any trouble reaching Napa, where I have
family.  I just let the Promariner charge the batteries overnight and
tried not to use the headlights.

Today, I finally got around to fiddling with it.  First, I started
the engine and measured the voltage at the starter battery at idle
and 2,000 rpm: 13.1V with the headlights off.

I pulled the regulator out of the Autozone
alternator.  Interestingly, its regulator was installed with
self-tapping hex-head screws.  Those sure look easier than the
straight-slot screws on my old alternator.

With some difficulty, I removed the regulator from my old
alternator.  The regulator is stamped "Made in Germany," if that
means anything.

The brushes in the old regulator look OK.  They're still pretty long
and have plenty of spring.  But I don't know how to measure the wear
or what the wear limit is.

I cleaned up the spring contact under the regulator with a piece of
scotchbrite.  It was looking a little tired.  Now it's shiny again.

I tried installing the new regulator on the old alternator with the
hex-head screws, but they're about 1/8 inch longer than the old
screws, and I could feel them bottom out as I carefully turned
them.  Evidently there's less room behind the threads in the old alternator.

So I went back to the straight-slot screws.  What a pain.  But I got
it installed.

I started the engine and measured 13.75V at the battery at idle and
2,000 rpm with the headlights off.  With the high beams on, it
dropped to about 13.5V.

I haven't driven anywhere yet, so I can't declare the problem
fixed.  But the initial results look very promising.

Again, thanks for everyone's advice on this.