I tried WD40 on it several times and nada -- nothing. Then I remembered a three year old container of Liquid Wrench by Gunk in the workshop. One drop and the nut came loose easily. Love it. Saved a lot of time, sweat and cursing.
I was not paid to endorse this product, nor did I receive any kind of encouragement or compensation to do so. I just love it when a product works better than expected. And yeah, I am a little disappointed in my old standby - WD 40. I think this definitively answers what is better, Liquid Wrench or WD 40.