Your diagnosis is probably correct, but more data would be a "good  thing".
Have you had any other problems due to a low battery?  One LED is a
rather flimsy indicator of the overall charging behavior.
Make some voltage measurements and report them to the list for evaluation:
  Battery voltage when it has been resting for an hour or so
  Battery voltage with engine at normal idle speed.
  Battery voltage with engine at about 2000 rpm.
  Voltage at the big red wire on the alternator at both above speeds.

By the way, you can pull out the brush/regulator assembly without
removing the alternator.

HTH,
Larry A.

Jon Kanas wrote:

> Good Day Vanagonites,
>
> The 1987 Syncro has developed an unusual charging behavior.  When as
> lower than average RPM (ie letting clutch out when leaving from a light,
> but before getting on the gas) the charging LED in the dash comes on.
> When the charging LED is on, the alternator is obviously not working
> (lights dim, reduced whine etc).  As soon as the engine comes over about
> 1000 RPM the charging LED extinguishes and normal charging returns.  It
> will occasionally flicker again at around 1800 RPM.   I have retensioned
> the belt and verified clean and tight connections everywhere.
>
> I am guessing that the brush pack in the alternator may be worn out ( It
> does have a brushpack / regulator screwed into the back of the
> alternator, right?) and need replacement.  Before I pull the alternator
> and check the brush pack etc, I wanted to inquire with the list to see
> if these symptoms might be pointing at a different problem.  Please
> advise at your convenience.  Any suggestions for obtaining a brushpack
> or replacement alternator also welcome.
> --
>
> Best Regards,
> Jon B Kanas
>
> Longmont, Colorado; Cultural Center of the Universe
> Email: kanas@qadas.com <mailto:kanas@qadas.com>
> Website: http://www.qadas.com/~kanas <http://www.qadas.com/%7Ekanas>
> AOL Instant Messenger ID: KanasColo
>