i have rebuilt my own alternators always, the core almost never fails, unless you short the winding, but it doesn't wear. Ball bearings are two, ne in the front ( bigger ) and one at the rear of the shaft, they cost about 12-15 USD each, regulators can be found for about 20 -40 USD, and brushes are 5 USD a pair. By the way, there is no comparison between an original alternator tan those sold by ebay, that are chinese, the splines shaft wears really fast, because of the low cheap Steel quality. So for me to swap to a chinese version is a second choice.