That's exactly what I do with all my meers - I was fortunate to be able to pick up the correct taps on fleabay a few years back, so I flood the threads with CA and then re-tap them...
Hole re-enforcers for notebook paper from the office supply. They come in paper and Mylar - two different thicknesses, so you can mix and match then as shims to get the right thickness. They slip right over the tenon and do the job.
They were both well colored when I got them, so I'm not sure what was smoked in them. Opium actually turns into a green color when smoked (don't ask me how I know...)
Look at it the other way around. Is it possible that the top half of the case caused the problem? Could someone have cleaned the top half of the case with a solvent which caused the damage which was later revealed by cleaning the stem?
I had to look up "bowling ball knife" - it's a machinist triangular scraper. Unbeknownst to me, I've been using a bowling ball knife for years, but never on a bowling ball...