Originally Posted by Morris the Cat
The correct bit is a posi-driv .
With the right one,take a plastic head shock hammer and sharply tap thru the screwdriver to loosen the threads.
Looks like a standard phillips head bit isn't
Mine were changed over to allen type fittings.
You can also dip the screw point in a bit of valve grinding paste if the tip doesn't fit perfectly. It will give you extra grip. The important thing here is the point must fit snugly, put pressure on it in anti-clock wise to release it, and then give it a sharp smack on the screw driver head.