From what I can gather from my extensive research recently in trying to source parts, and or part numbers. All I can tell you is that I don’t think they are designed to be serviced, as unlike car alternators there are no parts available for them,
I have dismantled and re-assembled the Denso Alternator with some ease, as it is modular in construction so bearings could be replaced, and possibly brushes, but nothing else.
Dismantling the Bosch alternator is challenging due to it’s construction, so any attempt to replace the bearings or brushes would likely lead to the failure or damaging the unit beyond repair.
I doubt many auto electric places would consider taking on the task without parts availability.
So you may be looking at either a new replacement, or a good used unit.
Hopefully someone will be along shortly to put me wrong.
Good luck
Ian