Great news Naki!
~Almost 14V is ok, probably more to do with battery/gauge than alternator. Its charging for sure.
I was wondering about brushes shape and their contact with motor recently too, although in the secondary water pump for cabin heating in my x300. Swapped brushes but motor was cutting out, as the brushes didn't make good contact with the motor shaft. I've taken it out again and sanded down shaft surface(there was a groove in there) for better contact and planning to swap it again, see if it improves things.
1997, 4.0 LWB X300 - Unlucky car but still a daily driver.
1988, 3.6S XJS - Never ending restoration project.
1994, 3.2S X300 - Accident damaged, October 2015. Gone!
1994, 3.2S XJ40 - Long gone.