The other component to ATF is acetone , and , yes it works , but will not help if that post is forced in. I would try anyway but add that a little vibration helps a lot . I take a small brass machinists hammer ( I made mine when I was an apprentice ) and tap the post rapidly for several seconds while applying copious amounts of the magic fluid with an acid brush . Don't pound , but gently tap to produce a vibration. Then let it sit for at least a day .....repeat. The last one I did (stem and post ) took two weeks but both came free and were still useable after polishing up. I learned this method after living on a sail boat for more than a dozen years . When things get stuck on a boat sitting in salt water , it gets very challenging to get unstuck without damaging things and this method saved my Irish a** more than once! Good luck , "The Journey Is The Destination".