Well, I can only speak to the Sitex coupler I worked on. It may well be
that you won't be able to open others. I simply speculated that maybe
they're built in a similar manner.

Mine had a nut on the bottom of the housing that I was able to get off. The
coax went through a hole in the center of the molded nut, and had some
sealant goop on it (probably RTV).

I figured what the heck----I was in trouble with that unit anyway with the
broken coax, so why not experiment? And, turned out I salvaged it.

The inside of my nut is threaded to accept the lay-down mount. You thread
the coax through the mount and then turn the coupler onto the mount male
threaded stud.