I was fortunate enough to learn how to rebuild and adjust regulators, back in the late 1950s when generator/regulator systems were just beginning to be phased out in favor of alternators. They're not that difficult to repair, but most "mechanics" who have entered the trade since the 1970's don't have a clue how either generators or regtulators actually work, or how to do the checks and adjustments necessary to keep them working properly.
Jerry