Windings shouldn't go bad. That would be incredibly rare. Brushes, bearings, regulators, and that should be about it. Now if we had permanent magnets like a one-wire alternator, then we'd have no problems with brushes. We'd be prone to GM problems though.
Thanks for the info on the VRs amc49, I'll have to go double checking mine, it would've been nice if you'd told us non-knowing peeps what colors to look for.
Now I'll have to search for the part number.