You should notice that the slip rings wear almost exclusively on one polarity. When i change the VR but not the slip rings i will change the polarity of the slip rings. Much easier than changing the slip rings.
https://xoutpost.com/bmw-sav-forums/...eo-alternaror-
My second valeo refurbish. I swapped the brushes and slip ring polarity.
I came up with an easier method to swap the polarity by cutting the conductive bars going to the brushes and soldering jumpers.
I think that method may apply to Bosch VR though i will see if i can find a photo
A couple photos to show how uneven the wear is on the slip rings.
If the VR simply swapped polarity every restart the alternator would last maybe 50% longer. (would make both the slip rings and the brushes wear evenly)