Paul, if they are the of the single 'oval' stem type, like my '97 Seven, then your problems may not end with getting them out. Once you've got them out getting them back in can be a nightmare. Getting the end of a squared off stem to slide into a squared off seat tube can be next to impossible. Solution I used was to file/grind a chamfer on the end of the stem to allow it to feed into the seat tube. Makes refitting the headrest a whole lot easier. Mind you, I am surprised that they are difficult to remove as your car is newer than mine so I'm wondering if they are not the same as mine, which has leather seats but I thought both cloth and leather trimmed seats of that vintage used the same seat frame?! The explanation might be that they have gone rusty as the chrome on the stem's is rather thin and soon goes rusty. As suggested previously, some WD40 or release spray might be the answer to that problem. I hope that helps.