I've been gluing valves back on a lot lately... they don't like heat!
I use aquaseal, 7 bucks a tube. I use hot tap water to remove the valve, dry it off then glue it back on... clamp them over night... all kinds of ways of clamping, I made a big round "washer" out of wood and then use a dinner plate with a 6lb medicine ball as a clamping device.
That's the easy part though... getting the bladder back in is the trickiest I find.
utube has a number of good videos on how to do everything.