non permanent loctite will work if that is what you have. 565 may be optimized, but based on empirical evidence that myself and numerous other members can provide, non permanent thread lock works fine.
Now, if you're going to try to get a non tapered screw to create a seal, or a non tapered crub screw, than you aren't going to get a seal. A tapered screw or plug will almost seal on its own.
If that little grub screw is loose fitting you might need to try to find a larger screw, possibly the screw is on the small side of tolerances, and the hole is on the large side (even without damage this can make a hole difficult to plug)
"I'll see it when I believe it"