Thanks for the replies. Yes, the unknown quality of rebuilds and generally declining quality in many new parts makes me hesitant to dispose of a potentially still good alternator.

Some more data:
I went and confirmed it is a Valeo alternator (on the label) - updated now in the first post.
In preventive maintenance several months ago, I greased the pulley bearings (I think one of cn90's many excellent tutorials) and replaced the OFHG (cn90 again, probably), etc. I checked the alternator bearings for play and noise and feel at the time, and don't remember anything of concern.

I usually get my parts at RMEuropean:
12317551153 12-31-7-551-153 valeo voltage regulator for valeo 90 and 120 alternators. $73.42, 2 year warranty
12317501599 12-31-7-501-599 NEW VALEO Alternator - 120 Amp (Compact) $298.97, 2 year warranty

Good prices (and free 1-2 day shipping to me here in CA), so either option will be OK. Since the Alt comes with a VR, I run the risk of having an extra VR if I buy the VR first and then need the Alt.

So I'm leaning towards giving just the VR a shot. Still deciding though ...

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2001 X5 3.0i, 203k miles, AT, owned since 2014