M & K 120

I have a green-and-black Pelikan 120, with a flat bevel on the cap band, a no-flare section, and a smooth piston knob transition, so, Merz & Krell. Big big chunks of old ink pile up in the window when I soak it. Trying to unscrew the nib collar, I pulled the nib and feed out. On the bright side, I could flush the ink chamber that way.

Once reassembled, the nib and feed don't seat deeply, they don't touch at the tip, and the nib swims and squirms. So, now I'm wondering...
Did I bust something?
Do I want to first continue unscrewing the collar, or seat-it and leave it?
How do I safely work the collar, if I DO work it free? I had only gotten about a half-turn out of the nib collar before the nib pulled.
Is that an ebonite feed? What's the collar? Is it brittle?
Is the collar 'set' to the old nib position?
geez, Did I bust it?

See, then it just circles around. I know that this is rather a baby step into vintage maintenance, but I could use some help. I like this little guy.