I can tell you the BMW dealer rebuilt alternators must use good parts (and they better for what they charge!). I have over 105k miles on my BMW dealer installed rebuilt alternator. I intend to keep my car long enough to make them make good on thier "lifetime free replacement" warranty. The "new" one that came with the car only lasted 81k miles...I'm at 187k now.
All speculation on what Bosch uses for their rebuilds, but at over $400 online for a Bosch replacement water cooled alternator for a 540, one would hope they use decent parts. They do offer a 2 year warranty...
Factory M-Sport with factory installed M-tech bumpers, factory Bluetooth, factory M-Audio 10" dual voice coil subs, homelink, M5 rear stabilizer bar, Bilstein B14 PSS coil overs, stop tech ss brake lines, Akebono Euro Ceramic brake pads, oem Brembo and Zimmerman rotors, Dinan Stage 1 software, strong strut front upper stress bar.