Those voltage numbers are pretty weak. I would expect 14 or slightly higher

 

The tested voltage is perfectly acceptable, especially see that you have a very strong battery. As far as rebrushing the regulator yourself.... Read about it and see what you think. I have been building starters and alternators for quite some time. Rebrushing is perfectly acceptable when the regulator is not faulty. The contact brushes only carry 2-3 amps, so the low current load makes it very cost effective to file and install a $5 pair of carbon contact brushes.

I dont sell rebuilt alternators...... The rewinding itself will run over $100 in some cases. I "refresh" alternators with a good cleaning, new or regreased bearings, replace the faulty part(s), and fresh paint. These are just as good, if not better than buying one new... And in your case, better than an aftermarket.

To answer your light question directly...... Replace with another motorcraft alternator or figure out what failed on your original and repair it.