All old Porsches have this failure, the wiper stops rotating but the linkage below the dash is functioning. What is the actual failure in the mechanism? a tiny metal rod or pin , thats all. the small cranks wont break they r tough metal, When i looked around to replace the units i only found very very expensive replacements, and its not a part common to the early VW like many other parts like the wiper motors, The actual unit is riveted together, assuming no one is going to drill out the rivets to determine the failure. ..So thats what i did,,, next time use a drill press to get the holes straight. Study the fotos and you will see the tiny pin that needs replacing ..thats it!then just get some nuts n bolts grease it and reassemble. The most difficult part is you just about need a toddler to climb under the dash to remove both assemblies,,i like working on old metal, iron , parts vs the chinese mystery metal or water bottle plastic all new cars are made of.