Search is your friend. And Sheldon Brown has a good article on it as well. Odds of WD40 working are just about zero. There are various levels of attack, from simple to more involved. The last step if nothing else works is to cut it out (very carefully of course). I have one I have been trying to free up for several months, avoiding the cut it out step. But that's next. I'll do it after I finish my other bikes first.