JB Water Weld
is my go-to epoxy for sealing up pressure leaks. My CPS 2000 also had cracks in the valve, so I put that stuff on it about two years ago, and since then it's been through several wars without an issue. My SS 300 had some serious leaks that I tried using everything from regular epoxy to PVC cement to patch, and none of them worked. Then I put on the Water Weld, and that was the end of that problem.
Only thing is, it's a pain in the ass to work with, especially when you're wearing gloves (and you should). It's very sticky.