Tear Aid Bladder patches are the BEST MATERIAL to seal leaks and small cuts in bladders. The patch can be cut into many smaller patches as well if pinholes are the problem, and TearAid will stick to any bladder with a really solid and usually instant bond.
The Bladder-Patch Install Kit which includes a bladder protection sheet and a 6x6-Inch (15.24 x 15.24cm) Patch. If your screw valve has to be cut out of the old bladder, then you need the Patch Install Kit.
Clean off area to be repaired with an alchohol swab
Spread out bladder and remove all wrinkles
Place Patch over leak making sure to not allow and wrinkles