Seems like the rubber has contracted and maybe a sign it's well past it's use by date. That's probably off an early 24 frame and reached 50 years of age.
Can you order them as a part? Otherwise, scavenge them off of Victa Vacs or other Super 24s and 600s with munted frames.

Nice array of metal tools in the pic BTW.

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!