The Ford Focus rear windscreen (windshield) wiper needs to be checked at least twice a year to make sure that the rubber compound that makes up the blade is not damaged. If the blade begins to peel or crack, you need to replace it. Replacement blades can be purchased from most auto parts stores. You'll need to buy a 13-inch wiper blade.
Lift the wiper away from the rear window until the wiper arm locks into a vertical position.
Swing the wiper up from the bottom so that the wiper sits perpendicular to the arm.
Press down on the release tab in the centre of the wiper-blade assembly.
Pull the wiper off the wiper arm.
Orient the new wiper assembly so that the bottom of the "U" in the centre of the wiper blade slides into the wiper arm lock. There is a tab on the top of the wiper blade assembly that will click when the wiper is secured to the arm.
Release the wiper arm and put it back in place.