I’ve found that before I try to remove the broken screws I do to things. When drilling the screw for a screw extractor I use penetrating oil, like PB Blaster, as a lubricant, which may loosen some of the oxide. Then before I try try to remove the screw, with the extractor in place, I heat the aluminum around the screw with a propane torch to slightly expand the aluminum. Works about 75% of the time.