I too am having some problems with a monitor.  The horizontal has shifted to one side causing part of the screen to not be shown, or if adjusted, appear on the other side.  The adjustments will not allow me to fix the problem. If I take the adjustments too far, the screen  goes crazy.... To be expected when reaching its adjustment limit.  It has plenty of adjustment to the left and right, it's just that the picture will not center.

Will a cap kit fix this? 

Even though I am NOT experienced with monitors, I am willing to give it a try.