SteveZ,
I learned a long time ago do not mess with that plug. It has been dragged over everything you can think of and most likely pressed the threads into something unlike a spiral. Now I just remover the cover to drain, if it starts to be stubborn. I have wasted a lot of my life on the $&?! things! Once, I had to remove the axle and turn it down side up, to remove the plug I had drilled through.