I've gotten many of these to come loose. I've also had two (maybe three?) shatter at the connection. The way I see it, if I'm willing to leave it stuck because I'm afraid it will shatter, then I might as well attempt to take it apart and if it shatters, glue it back together and I'm where I would have been anyway.
My success rate in getting them apart when they are 'well-stuck' is about 95%. The most successful technique has been to soak the thickest pipe-cleaner that will go past the connection, in alcohol, and let it sit in there for a few hours. Remove it carefully and then very carefully try to turn the stem. If it is going to come loose it will just barely, barely budge the slightest bit very quickly. Don't force it. Repeat with a new pipe-cleaner, then try again in a few hours. I've done this three times on a few occasions before it finally worked. I also have several meers where it did NOT work and I gave up and left the stem stuck. But...I will go after those again some day. I have probably done fifty of these and only had two break that I can remember - a bone one, and the following amber tenon.
The other day I had a very surprising 'fail'. After the second pipe-cleaner it began to budge a little. It felt exactly as it would if I were going to have success. I unscrewed it gently and it had apparently shattered at the first twist. The good thing is that the 'shatter' is almost always the tenon breaking off - not the amber stem. This one shattered because the tenon was actually part of a one-piece amber stem - not bone. Bone is stronger and almost always survives (in my experience).
On rare occasions, when the above didn't work, I've put the pipe in the freezer and it's loosened it enough to unscrew. But the freezer technique has a higher success rate with stuck briars.
The key is patience. If the stem was glued to the shank with CA glue, you can forget it. You won't know it, of course, but it will never budge without breaking.
Absolutely true
