Just performed a loose stem repair to an old Rossi of mine and worked like a charm...then did the same to 2 cobs I have and worked great on those as well.
Took boiling water and poured it into a small bowl to about 3/4" deep, took a worm/screw clamp and clamped it around the mortise of the shank with some electrical tape around it and screwed it down nice and tight. Held that in the water for about 2-3 minutes until hot, then I tightened on the screw a little more to make sure the wood was malleable--i.e., hot enough, inserted the stem and kept tightening until the stem was as tight as I wanted it. Let it cool completely for about 10 minutes and took the clamp off...worked great, FYI.
Took boiling water and poured it into a small bowl to about 3/4" deep, took a worm/screw clamp and clamped it around the mortise of the shank with some electrical tape around it and screwed it down nice and tight. Held that in the water for about 2-3 minutes until hot, then I tightened on the screw a little more to make sure the wood was malleable--i.e., hot enough, inserted the stem and kept tightening until the stem was as tight as I wanted it. Let it cool completely for about 10 minutes and took the clamp off...worked great, FYI.