I had the voltage regulator replaced at about 185,000 miles for preventive measures. I did pull the old one from the 70AMP alternator and the brushes had about half an inch of length to them and still nice and springy. It was the KAE brand, and I kept it for my box of spare parts.

So I do not think the voltage regulator was the problem, or have you had a voltage regulator fail at about 15,000 miles before?

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2006 BMW M5 "Heidi" @ 109,000 miles
2005 MBZ C55 AMG "Lorelai" @ 165,000 miles
1991 MBZ 300E "Benzachino II" @ 165,000 miles
1990 MBZ 500SL "Shoshanna" @ 118,000 miles

(On the hunt for a good used M103 engine as of 6/10/23, PM me if you have one to sell!)