This is on my daughter 85 300D, she said there is a squealing noise some times when she depresses the accelerator pedal.
So I checked the belts and the 2 belts on the alt are sloppy.

The manual said to loosen 1 nut and 2 screws, 1 nut & 1 screw on the top side of the alt, tight squeeze to get in there but they are loose, now screw 2
is on the bottom side of the alt and this screw needs a star headed Torx which is shown in pic#1&2, anybody know what size torx?

Then come to find out the tensioning screw is broke and there is no tensioning nut pic #3 & #4 ( number 4&5 in the pic)

I'm sure I can snug it up enough with out the tensioning screw/nut but it would be nice to know what size that torx bolt is so I can loosen it, I'll need to buy that size.

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No, you'll not be able to get it "snugged up enough" without the tensioning bolt, its critical for proper adjustment. Don't mess around with it and either replace the tensioner bolt, or have a mechanic replace/adjust it. Loose belts can lead to overheating as those belts also drive the water pump and fan, they need to be at good tension. Do the job correctly and fix the broken part, or be sorry later when something far more expensive (engine), gets destroyed.

There should not be a torx bolt on the lower part of the alternator, thats the wrong bolt if that is whats there. Should be a normal 17mm hex.

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Yes, I plan to replace the the the tensioning nut & screw.
But this bottom torx bolt sure looks original!

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It's quite common to mistake a 12 point metric fastener for the Torx. They appear to be the same, however, a Torx will quickly strip the fastener.

I had struggled with a Torx on the rear diff fastener of the SDL and nearly stripped it. The proper Hazet bit, a 12 point metric bit, removed the bolt with no effort.

If I was a betting man, I'd say that the bolt is not Torx.

so you think it's a triple square / xzn bit?

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I'd bet on it........

I don't believe that Torx appeared on any M/B back in the middle '80s.