I find the screws loosen under hard use. I have thought a lot about this as I know common knowledge is no Loctite is needed on a 21. I use my sebby's a lot on weekends sharpening sticks camping, and during the weeks sometimes stripping cables etc. The screws tend to loosen for me when I am applying a lot of torque on the handles, thus twisting the slabs away from each other in my grip. I think over time this slightly shifts the screws and they start to back off. I notice they are loose when the knife starts to rattle. My 25 does the same thing (The back-spacer screws without lock-tight) as does both my large 21's, and the back-spacer screw on my Umnum. I don't beat on my small wood-inlayed 21, so it stays tight. I have come to believe people's experience may vary depending on what they are using the knives for, and how much twisting of the slabs is going on.
What I have decided for myself is I would rather use a small drop of light duty Loctite, that torque the living daylights out of the fasteners to keep with CRK tradition. Being a tradesman, I hate to see everything get all galled up, think about all that unnecessary stress on the screw threads, and wear out the hex head, when a little Loctite is just fine. They put military jets together with Loctite. I have no issue with the product, though you have to have it on hand.
