Intersting thread. The glue I use depends on the material I am turning. I use gorila glue on all wood and antler pens. I use thick CA on all acrylic and bowling ball pens. I have never had a glue joint problem with this setup.
As for the glue in the tubes, i use sheets of dental wax that i twists the pen tube ends into. I can't tell you were to get it, my wife brings it home from work for me. But, it works great.
Gregg