Maybe I missed a turn. How is air getting in between the stem and the bowl? You mean the shank, the slender briar that comes off the bowl to meet the stem? Any break in the airway will cause a bad draw and maybe overheating. Medico did make many Brylon pipes, a synthetic (wood composite?) that famously burns hot anyway, even without the crack or hole in the airway. I think it's time for a new pipe. If you're on a budget, I highly recommend MM cobs, about $5 to $15, or if you can pay a little more, one of the MM cob special series with an acrylic stem that lasts a lot longer, at about $24.