The Pelton & Crane headrest glide allows the headrest to slide up and down without turning sideways. It requires pulling off the 6 screws that hold the top upholstery on, and removing the old glide. Then installing the headrest glide, and reinstalling the upholstery. Total time should be less than one hour and experience level on a 1-10 scale with 10 being difficult is around a 3-4.
These parts are not commercially available, so I began making them off my CNC out of a solid piece of Delrin. They are much stronger than the original piece, and come with a one year warranty.