Once I had decided to use Loctite, base on previous discussions over the years, and my own experience of need to use some type of adhesive, I wanted to use the best product for the intended purpose. Red Loctite was designed to provide a strong, fairly permanent bond. So I tried a test, to see if the bond could be broken without destroying the pen, when the need to disassemble would arise. I found that I could break a pen down after using the Red during assembly. So Red Loctite is what I use every time, unless the fit is so loose that epoxy is called for.
I want to clarify and add info to my previous post. I talked about using Loctite on every pen. I do limit that to the press joints that serve to secure a clip. For the remaining joints, I am selective, and use it (or not use it), based on my prior experience, and how tight the fit feels. The other joints are often not heavily stressed, and just need to stay together. They are not critical as are the clip-holding joints. I do use the Red Loctite on all thread assembly joints.