Some more information on this machine
It had been unwired to remove from the cabinet (they did not cut the wires, and they are in good shape). Since it had no cord or foot pedal, it was sold as "non functioning". With the shuttle in place, there is a noticeable vibration and a "grinding" sound when you turn the flywheel as the hook is coming up to the top. I can only imagine how horrid it would have sounded if someone ran it with power before removing it from the cabinet.
We took the shuttle out and the noise and vibration go away - and we noticed a lot of powdery residue around the shuttle race. I'd say "rust" except it doesn't look like anything is rusted. More like someone put something around there for lubrication, and it dried up and turned to a light orange powder.
Over all, the machine working parts look like it's seen very little use - less than any of the 15's we've encountered so far. We figure all it needs is a good cleaning and some oil.
The seller did not have anything in the write-up about this being a "special" machine in any way. Just a really nice old Singer sewing machine. Starting bid was reasonable. Based on what I paid, the people I was bidding against also knew what this was, but they didn't want it as bad as I did (yea!).