I never glue mine. Do you have the proper pad? It should be at least 1/4 " thick, and between the rim on the piston and being captured in the chamber, there should be no problem, as "ford38V8" said.
I searched for a long time and was finally able to purchase a piece of 16 oz leather (the thickest available, 1/4" thick). I bought the proper size hole punch (I think it is 5/8") and make my own. It takes a lot of pressure to use the punch, and a hammer blow usually doesn't do it, so I use my press. I had to buy a 12" X 12" piece of leather so I have some left. If you need a new one let me know.