Its most likely threaded. Try one of those rubber discs you use to get off tight lids on jars.
I would first . . . . "lube the crack" . . . so it can run down to the threads.
Put screwdriver in vise with rubber for protection. More rubber on the top and use vise grips on it. Good luck.
Another trick is to hit with some vibration. Get an impact wrench or air hammer going and hold the handle to the side/body of the air tool.