An update helpful for future reference.
I checked the car again to make sure all belts were tensioned properly, and realized something new: the slippage in the tensioning mechanism was/is not due to damaged teeth in the star bolt/toothed bracket after all....but rather due to the toothed bracket rising when turning the star bolt, thereby causing the slippage. It seems that no matter how hard I tighten the bracket's bolt (I used a breaker bar and believe me it is super tightened), it will still rise when attempting to tighten the belt via the star bolt..... So I pushed the toothed bracket back down by use of a prying bar and retensioned the belt as best as I could. Everything is fine, and the belt was holding proper tension even before today's tests.... But I suspect that many of those on the forum who claim slippage of this type of tensioning gear due to damaged teeth, in reality have this same problem: the toothed bracket rises when turning the star bolt.....which causes the slippage. Just letting everybody know, should you face a similar problem with the gear mechanism for tensioning the alternator belt.

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1979 240D, W123, 105K miles, stick, white w/ tan interior.