Even better than WD40 (which sucks as everything equally) is a mix of ATF and Acetone for stuck bolts. From the store, pb blaster is the best. Wd40 stands for Water Displacer, it is not the formula our fathers knew. They would have used wax and a torch or wintergreen oil anyway.
Corollary: No amount of force or increase in cutting speed will substitute for bad planning. (from my metal working guru friend)