After using the penetratingly oil, put an old 1/4" router bit or an old 1/4" drill bit in it and tighten it down, then tap the bit gently with a hammer or a block of wood. It's real possible there is a bit of rust in there holding it in place. Then loosen it a bit and tap the bit gently from the side as you rotate it.... i've had this happen myself on an old router, and got it free'd up. Kirk