I've been doing more research on this and it appears that the "Premium" Bosch rebuilt alternators do, in fact, use German-made parts. While all of the individual components that I've been able to find so far except for the bearings have questionable origins. It doesn't make sense to go to the trouble of removing the alternator and cracking it open to only change the bearings. Might as well do a full rebuild.

If I can find a source for the Bosch parts, I want to rebuild it myself - it doesn't look that complicated. But if I can't find authentic parts, I'll have to go with the rebuilt unit and hope that it really does contain the parts they say it does.

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2002 X5 4.6is - Imola Red/Black (Sold)
2001 740i M Sport - Anthrazit Metallic/Black (Sold)
1998 M3/4/5 - Technoviolet/Dove (Sold)
2003 Z4 3.0i Sport - Sterlinggrau Metallic/Black (Sold)
2009 Mini JCW (The Wife's)
2015 i3 REx - Arravani Gray/Tera World (Daily Driver)