I've had recent intermittent problems with the charging system on my 2001 3.0i E53 with ~174k miles, AT, very good condition. I have the original 120A air-cooled Valeo alternator (BMW logo on the label and no service records to indicate service, so I think it's original).

I'm looking for advice or specific diagnosis help to determine whether it is the alternator or just the voltage regulator. I think I've got it narrowed down to one of those two.

Symptoms:
Intermittent charging, steady, good voltage when charging works: 11.x V when engine running but not charging, then jumps to a very steady 13.3-13.4V, independent of RPM, when charging is working. From reading this forum, it sounds as if 14.4V is the charging "spec" as is normal for most cars, but that ~13.5V is actually normal and just fine for these cars. Comments?

Intermittent unfortunately in this case means it works just fine a small fraction of the time, but mostly does not charge. So it's definitely in need of repair, but the fact that it sometimes works "fine" may help in the diagnosis.

There is no middle ground - it's either charging at good voltage or it is not charging at all.

The charging warning light appears to be working just fine, based on voltage measurements at battery terminals and via OBC test 9 (which match eachother). I.e., the warning light comes on when it is not charging, and goes off when it is charging properly.

The battery appears to be just fine - can be charged with a charger and holds 12.x V.

No other problems with the car.

No bad noises in the alternator area.

Belt, pulleys, PS, oil filter housing gasket, etc. are all in good shape, maintained.

Do these symptoms point to the VR vs. the Alternator?

At my 170+k mileage, but no bad noises, should the alternator be replaced anyway?

Is it worth a try to just replace the voltage regulator on this one? I'm a believer in leaving working components alone if possible, but I will have no problems doing the repairs myself.

Thanks

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