There are a couple of you tube videos showing the correct way to put back the stopper pins. One of them needs a tiny rubber sleeve over it before you re -insert it in. I successfully did it a couple of times but have now forgotten the fine details sI haven't done it with enough repetition to learn it down pat.
It really is a terrible design.

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