This is not a difficult repair and for the Valeo 120A alternator popular in the 3.0 gas model, it's a bit of a no brainier.
Here's the basic problem; the one slip ring gets 80-90% off the wear. The matching brush also gets more wear, this leads to too little force/pressure on the contact area and the alternator can't output at low RPM.
https://www.icloud.com/sharedalbum/#B14JsHvHoGjXxga
My photo album of the repair job. You can find the slip ring kit on eBay or many websites (not Amazon). You can find some YouTube videos with more step by step, I only have some hints at the major steps.
The key thoughts: use heat to remove the epoxy potting if you replace the slip rings. I'm likely to just swap the two brushes and make a no part repair, something I was hoping to do preemptively but wife's alternator decided to crap out before I got a chance.
I figured out a way to swap the polarity of the brushes which will stop the wear of the high wear slip ring and I'll show pictures of the fix.
If you copy the trick somewhere around 4000 hours you should get at least 8000-9000 hours out of your alternator as long as the bearings hold out. (I estimated 5000-6000 hours on mine and wife's before slip ring replace on mine)