The wiper's pin that makes the vertical up- and down movement possible, has to be lubricated regularly (we normally do that during every service...) to prevent the system from getting a hard time (as described).
If you remove the black plastic cap (start pulling at the bottom, whilst widening the cap, and rotate out the top) you will see the metal colored wiper part as in the picture above. In the middle is a pin that will go up and down when you (manually) turn the wiper over the windscreen. Clean and lubricate it when it is in the most extended position.
good luck & greetingz,