Today I repaired a broken front passenger headrest, it used to flop fore and aft. After dismantling it I discovered there were 6 pieces of broken plastic bits which I plastic welded back in place and reassembled the whole unit and adjusted the tension clamp. After that exercise I looked at the driver headrest and found it was very stiff, rather than force it I removed it and backed off the tension clamp i until it was free. NOTE if you want to avoid dealing with all these broken bits I strongly suggest you carefully check the fore and after movement of your headrests.........if they don't move freely DON'T FORCE them, remove them and open the bottom upholstery which will expose a Torx head, back it off until the headrest moves freely, then adjust the tension until you find the movement that is neither very stiff or too loose.