I have Sheaffer Sentinel [non-snorkel] with the Touchdown filing system. Found at a junk shop. Nice conical nib <F> that writes well when I tested it by dipping.
Disassembled the section from the barrel and found the ink sac was crumbled. I managed to clean most/all of it out.

Problem: The metal ink sac protector is frozen about a quarter of an inc up inside the metal vacuum tube. Have had no luck trying to dislodge it, so I can't continue to disassemble the plunger knob from the barrel and attempt to push out the protector from the plunger cylinder by pressing it out through the attachment knob screw hole in the cylinder. I'm down to considering cutting the tube and protector off, just below the knob with a Dremel cut off wheel, and working from there.

That would, of course be dependent on being able to find a replacement plunger tube and sac protector.

Any ideas about another way to proceed... or hopefully a resource for finding a replacement protector and plunger tube?