Also check that the earths, battery, and alternator connections are all tight, and that the plug on the back is pushed all the way in.

Replacing individual components depends on the condition of the slip rings, the bearings and the ability to get the fasteners out.

I have reconditioned a few alternators, and have also made and fitted a simple-to-build regulator to some. One alternator beat me, because each screw that held the delicate components was seized.