Rub some candle wax....any wax, all over the tenon to act as a lube. I rub wax on the tenons of every pipe that I own, and I try not to remove the stems from my pipes when cleaning....I just run some pipe-cleaners dipped in high-proof drinking alcohol, down the stems for effective cleaning. Brandy, Rum, Vodka, Moonshine, Rum Extract....all will work. I would not use Isopropyl, rubbing-alcohols, which might contain scents, and Glycerine. Yech!
That extra tight tenon may just need to be slightly rubbed, ever-so-slightly, with a piece of 600-1000 grit sandpaper. Make sure you only sand the tenon of the pipe stem, and stay away from the stem/shank interface. Just a whisper of sanding with an ultra-fine grade of sandpaper will most likely be all that's needed for a better, less tight, fit. Sand very, VERY, gently, and try the fit with some wax rubbed onto the sanded tenon. Sand only until the tenon/shank fit is perfect.
Try the wax treatment first.... sand, only if necessary, last.
Good luck,
Frank
NYC