I have a "junk drawer find" Sentinel. I have disassembled it and cleaned. The "sac' had deteriorated to chunks inside the metal sliding " vacuum tube, but managed to get it cleaned out. However, I can't see or feel [with a screw driver] and screw to disassemble the end cap/knob from the metal tube.
This didn't have a sac/bladder protecter (as some other vacuum filler Shaffers do) just the remains of the rubber bladder.
Does this sound normal?
Just takes a bladder without a protecter?
Suggestions on where to purchase bladder tubes [ or a protector sleeve is there is supposed to be one]?

No history to the pen.

This.