Sounds like your brushes are worn out.
Either my local O'Rielley's or Napa can still order the Motorcraft external regulator. (Can't recall. Usually have it later in the day or next day.)
Also Powermaster makes some great rebuilt heavy duty alternators. They are pricey, but if you are going for longevity I would take a look at them. Popular in the Jeep community for taking a beating, getting dusty, and high loads.(Winch, lights, etc.) You may have to put your double pulley on it to use it. They tend to sell most alternators, just not with all options. (Back plate at 3 o'clock instead of 12' o'clock. Double pully VS single pully.) The alternator is the same, just not set up the same or with the same pully. But this all can be done by the buyer.
http://www.powermastermotorsports.com/
If doing the Alternator adding a $30-40 regulator just makes sense. If nothing else cheep insurance that both will go the distance again. Some auto parts stores can still test these external regulators to confirm good or bad, but I would recommend just replace with a new Motorcraft one.
Ditto to rebuilt auto parts store alternators are hit or miss. O'Rielly only had their cheaper chicken house brand for my sons 67 Galaxie. First one had a bent fan and was out of round. Second one had a loose pulley. Third one the fan spun when you held the pulley. We said heck with this junk and went to our local independent auto parts store. Theirs at least did not have any visible issues. We will see how it holds up. What happened to pride of work and quality control????
We had a great alt/starter rebuilder locally until recently. He did marine and automotive applications. I believe he closed down due to a rental increase and decided to retire. (Had already moved once a couple years earlier.) Went to the other guy, was not super impressed with his shop or work. So I will have to find another good rebuilder.
We also lost a great trailer repair shop, developer bought the property, owner could not find another property around for close to the same rent. He went to work for another trailer shop a few cities over. We ended up loosing a key small business withe tons of knowledge for apartments or town homes adding to the cities already heavy traffic!
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