I have an old(ish) Butz Choquin billiard that had a loose stem. It wasn't so loose that the stem would fall out, but was pretty easy to rotate and remove when the pipe was cool and dry. While smoking, the heat and moisture would cause it too tighten up a little and be just fine.
I tried carnauba wax (as I didn't have bees wax). It never seemed to be a permanent fix though...the stem would always loosen up again after a few smokes.
Eventually, I tried the clear nail polish technique (after somebody on this forum suggested it). Worked like a charm and haven't had any issues since.
Should be pretty obvious what to do, but...
Apply a light coating of the nail polish to the stem tenon and allow it to dry
completely before reassembling the stem to the shank. Don't want to permanently glue the stem in
If the buildup of the nail polish creates too tight of a fit, sand it down lightly with some emery cloth. If still loose...add another coat.