The trigger bar is made of stamped steel, and is not perfectly flat , the curve is not visible to the eye, but does effect how it rubs against the plastic. The curve itself is not that much of a problem, I would say the bigger issue is the roughness of the surface where it rubs. Using #800 sandpaper to get the surface treatment off and flatten the surface, then #2000 to polish it to a mirror finish removes most of the friction on the plastic.
I did not see any glue, but I did install a CGW pro kit so a bunch of internals were replaced and not inspected. I also polished the trigger itself, and the assembly pins, and the sear. My trigger now has 0 stacking, I mean absolutely 0, you cannot tell it is going to break until it does. It is glorious