Hi John,
I always use the bottom of my tennis shoes when I have a problem getting filters apart, just press firmly on the flat of the shoe while wearing it and turn firmly, seems to work almost every time.
I have also put a small amount of candle wax on the threads in the past to help lubricate and keep them from getting stuck, I just run the thread portion on the wax and then remove any excess with my fingers, it does not take much at all, but it sure makes a difference when I need to get them apart.
Dave