I have taken off the heelpiece and and ive taken the two screws i can see from the two piece but they are still held on by a third screw somewhere that i cant find. is it underneat a plastic cap that i have to take of with a different screwdriver? i cant find a screwdriver to for the screw on the top and i dont want to waste my time finding one to fit if thats not what i have to do..?