Rutger,
for the purposes of getting a grip on the knurled nut, you may be better off going in from below, taking down the wiring harness, laying on your back on the floor, and contorting your hand and arm up through the dash. Taking it off is much easier than putting it back on. Try using a rubber thimble on one of your fingers for more traction. Also, don't take any blood thinners before attempting this, as you may risk bleeding out.
Good Luck,
Mike Mizesko
Columbus, OH