I went ahead and fabricated a plug/cap.
My first idea was to try and make it out of Delrin or a plastic that was similar.
The problem is that working at such small sizes, the heat of the lathe cutting tool was causing the pieces to deform.
I tried several pieces, and I was getting no love.
I realized that my original measurements were accurate, but because of the MZ-S cap being made out of rubber, the cap was slightly larger than the opening on the camera!
When I realized that I was going to have to do something different, as in use an 0-ring to give friction against the cap and the MZ-S body, I tried another design.
Finally I got it right.
Notice how o-rings are not perfect either!
Look at the detail of that o-ring close up!
Where the cap/plug is going!
Nice - Bling!!!!!
Bling! Bling!