Installed a new fork, headset, and stem on my Kestrel with Integrated Headtube.
While trying to load/tighten the headset, I noticed that the Top (bearing) Cap of the headset was not sitting flush with the Upper Bearing Cup. As I rotated the fork, I could see the Top Cap "wobble" (i.e. the gap between the cap and cup would grow and shrink.

I found that it was my stem that was causing the problem. The bottom (and top) surface of the stem fork clamp was not perpendicular to the steerer bore axis. I don't believe this is a manufacturing defect, but a design flaw.

Can a stem be "faced", so that the surface that mates against the headset is perpendicular to the steerer axis?