Gunter, try a new rack first. They are still used today, Defender items fit, they are available and cheap.
Also, a tip. When you pull the old rack out, the wiper spindles will rotate in unison, suddenly stopping when the old rack disengages. Carefully turn them 180˚, and make sure the replacement rack is exactly the same length before you feed it back in. It will thus work on a fresh, unused sector of the wiper spindle, and should remove a lot or even most of the slack. (Unless someone has already done it of course!). It worked for me, and meant I didn't have to go any further.