You can do what Slick did and replace the voltage regulator with a new one, that includes the brushes and can be done for about 110, go on ECS website the BMW part number is there in the alternator section.

I see new Bosch alternators and Valeo's on ECS Tuning for around 250, did you double check to see if you have a 90a or 120amp, and do you have a Bosch or Valeo?

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards