gary wrote:

The stem did NOT break cleanly so the broken surfaces do not align.

You mean pieces are missing and/or you can't figure out how to put
Humpty back together again.

Why can't I use a diamond whetstone to get two flat surfaces that I can then glue together?

Feel free. It'll work, but do me a favor and keep a log of the time
you spend getting the two surfaces to mate better than they do now.
Oh, and take before and after pictures so we can see the improvement.

You do understand that you're basically asking, "Hey, I had an
accident with my car. How much time will it take to fix it?", right?
If you posted a picture I'd be better able to tell you if you were
going to waste a little time or a whole lot of time.

R