[wwest]

At the very heart, core of alternator use technology, was/is the requirement for SIX high power 80 amp SOLID STATE semiconductor diodes with greater than 50 volts reverse breakdown voltage and EXTREME heat tolerance.

No alternator automotive battery charging/voltage supply system could be possible without those.

Now, I go back to time of/for drilling the rivets out of the old VR case in order to "refurbish", file down, the voltage regulating relay contacts. These contacts open and close at a rapid/variable rate in order to supply the PWM rotor current for correct battery charging, ssytem supply voltage under all conditions.

Each and every time those contacts open the resulting inductive voltage "kick" removes a few molecules from the relay contacts. Very much like your Kettering ignition points, if you've even taken a good look at those upon replacement.

For how many miles was that mechanical VR good for? Like clutch wear, that depends...

How many open/close cycles has a given pre-1980 era VR had at 20,000 miles.

In my experience replacing the VR was in the range of 20-30,00 miles.

Note: Nowadays you can buy a solid state VR that mounts outside the alternator..but can you buy an alternator that requires, uses, same...?

To my mind there is no viable substitute for a modern day alternator with internal (solid state) VR.