Lots of good tricks mentioned now.
Spray can stuff like PB blaster penetrates just about any hint of a crack or space, even horizontally. Screws can still be subborn, so I guess it's about letting it seep in and do it's work. Sometimes I have had luck by switching to a different oil. I usually have some kind of spray can stuff around, the basic oils I use tend to be Triflow or Finish Lince Ceramic Wet Lube around. You should in theory do very well with the stuff you have mentioned; PB blaster and the basic sewing machine oil.