Re: So why rebuild rather than buy a new generator
I've only heard a few comments on the "new" generators from Moss (actually from China, as I recall), and they've not been terribly favorable. Thing is, original Lucas generators seem to be almost infinitely rebuildable. In reality they often need no more than brushes and cleaning of the commutator; sometime, though, they'll need a bushing or other bit...and most of those "bits" are still readily available.
There is a major parts vendor that makes some "fuss" about buying a rebuilt, noting that you don't know how many times it might have been rebuilt or how well, etc., etc. From my experience, these units tend to last a very long time unless something mechanically breaks or the whole thing fries so badly that the armature or the magnets or field coils are shot. But at worst, one can usually make at least one good generator out of two "iffy" ones and a couple new parts. (You can easily get brushes for a typical C40 Lucas generator from NAPA, although they'll likely not be in stock at a given local store.)