A guess but I think the threads have stripped.  If so the only solution is a new stem.  @JerseyMo, we need your help. 

Welcome to the WRT forum.   

Case tube... thank you for that 🙂 So I took out the stem again and I took a picture although its hard to see, and it looks like there are vertical groves over about 2ishmm of the end of the stem with .5mm of clean metal at the tip. Im wondering if there are companion grooves inside the crown and that is what is supposed to help the crown stay in place? I don't see how that would help with pressure being applied away from the case but I thought I should mention that just in case and post a pic along with it. 

I would like to replace the bezel insert of a 1985 Seiko 5H26-7A10, I was wondering if anyone knew the exact measurements of this circular ring, since from my measurements I detected 36 ext. - 30.3 int. While generally inserts are found 36.5 ext. - 30.5 int.

The problem with buying a super clone to experiment on is the cost several £1000 .