A hint for removing stubborn screws... After soaking with your penetrating fluid of choice, use the LONGEST shafted screwdriver you can find that fits. The additional torque that you can apply through the longer shaft will help remove screws that you cannot budge with a shorter screwdriver. Also when trying to loosen a screw that is stubborn, push down as well as rotating.
NOTE of caution: a longer shafted screwdriver can also be easier to lose control of, slip and scratch your machine.