Interesting, I have not heard of this product before. Reading the descriptions seems to imply the Loctite products are for metal to metal threads, had anyone tried this with rubber to metal?
Now I'm confused: isn't the threaded part of the eyepiece made of metal? All it takes is a drop or two, so if you're worried from the possible consequences of the contact between the Loctite and the rubber part you can be careful and just "paint" a bit of the metal thread on the far side, avoiding the rubbery section.
If instead the thread itself is made of rubber, or rubberized, than sorry but I've no experience in this regard. Maybe you could ask Loctite's (or one of the other manufacturers) customer service directly?
I use this kind of product in situations where vibrations can unscrew a piece, mostly on bicycles or on the screws that keeps my tripod locks together*.
*Not necessary for general use, but I keep an heavy tripod in the trunk of my car at all times, and the vibrations tend to unscrew the locks with time.