Thank you for your help thusfar.
With Tri Flow, then heat (from a soldering iron), then a light tap-tap, then a firm unscrewing with screwdriver, I removed six of the seven tiny wee screws. I cleaned things as well as I could, but did not find any major debris which I could blame for the bind-up.
So, then I removed the large-ish three set screws which keep the whole bobbin business on its rotating shaft. I marked and photographed carefully as I know I will need to fine tune the timing upon re-assembly.
Found a heckuva thread wrapped all around the shaft! Cleaned the two gears which mesh together, reassembled everything. So, I have now disassembled and cleaned EVERY BIT of the bobbin business -except- for the one "brackety bit" which has the deviant screw which will simply not come undone. However, things are -very- clean, and because that tiny screw is screwing the bracket to the main part, I figure that if I flossed in and all around that one stuck screw, there cannot be excess debris, right? Do you follow my logic - I mean, with the screw screwing metal to metal, it is hardly as though thread will pass through there anyhow, right?
So far so good?
Then I replaced it all together, but when I replace the finger, then suddenly I am back to square one. The needle bar will then not move up and down, and the bobbin business remains stuck in one spot.
So, about this finger:
On my Singer Clone, that finger is built into the bobbin case.
On Ziggy The Phoenix, that finger is attached (screwed) to the machine underside.
That finger serves the same purpose in both cases, right? To allow a bit of left-to-right movement while the hook oscillates?
What could be causing the whole works to seize simply by adding the finger to the equation?
There must be some mechanical operation that I am not understanding, for I just cannot figure out what could be the trouble. Please and thanks, I have really appreciated the help thusfar and I will be so happy if I can fix this guy.