Actually, I'm not sure you absolutely have to have it. Have you tried holding the hand wheel and tightening the knob as far as you can? It sounds like the washer is in the correct position as it did sew some. The screw just keeps it in position so that it doesn't unscrew all the way off. I think there may be some that actually screw into the washer, but not yours. It should be like the links like I sent before.
I'm pretty sure you just tighten the knob finger tight and then put the screw in. Someone described the purpose of the "pin" "screw" at
Stop Motion problem
I hope you can find it.
There aren't many sewing machine repair shops around, but you may be able to find one that has an old parts bin that may have one. There are new ones available, but several different sizes. I could try removing one and tying it in another machine - it isn't like I don't have a variety of machines to test
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Janey - Neat people never make the exciting discoveries I do.