Need some assistance repairing a Columbian bench vise

I bought this vise new about 30 years ago or so (Columbian model D56 w/6-1/2" jaws), but I don't recall where exactly (Sears, Home Depot, Northern Tool, ???). Worked great, and served me well/fit my needs, but when I sold my first house and moved in 2011, something "let go" inside, and after that happened it still tightens up just fine, but it doesn't "loosen up" (the jaws won't retract when I turn the spindle out).

I got really sick of it just now, so I tore it apart:

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Looking online I see all sorts of different mechanisms (collars, clips, etc) used to hold the spindle into the "moving portion" of the vice, like this one:

View attachment 1716370873

But I can't find a diagram that shows a spindle that has two grooves, and uses a spring:

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There was a sheared-off pin inside the vice:

View attachment 1716370884

But I can't see what it goes. (And it may just be a shear pin from an old snowblower!)

Is anyone here able to offer some advice/assistance on what I need to repair this thing? I'd rather not buy a new one, as 1) I hate wasting things, and 2) This one still does the job for me/seems to be heavy enough, so I'd like to fix it.

Thanks!

Jim
It probably needs a vise nut. I used to stock them on my tool truck. Examine the threads closely inside the nut. The screw threads rarely wear out enough to cause an issue.