If it’s only a friction issue, if you smear your little finger with some 3 in 1 oil, and poke it down the hole as far as you can go, you will touch what feels like a roller of some sort. Rub the oil into it. Also wipe over the headrest stems with some lubricant. Work it in and out a few times. Wipe off any excess and it should have improved.
Beware also of withdrawing tight headrests. Some people have found that following a big tug, the headrest has flown out of the hand and landed on the bodywork!
