The WD in the name stands for Water Displacement. What you need was mentioned earlier - slather it with vinegar or CLR, or something similar. Do it periodically over say a day or so. The acid will break up the mineral deposits that are holding things together. WD40 (the 40th try to make it work as a water displacement) is not designed to loosen a mineral welded plumbing fixture. If that doesn't work, it may be time to cut it off.