Georg;

I guess intermittent wiper are only a good thing to have when its by design and you turn that function on!

It sure sounds like the "home" switch in the mechanism may be worn to the point of being intermittent...after making sure it's not the panel switch (wiggle, tap, talk nicely to, insult, etc.), you may want to extract the wiper assy. (removal is not that bad after you first disconnect heater control pod from dash), open the cover of the "home" switch and inspect. If you find it's worn, repairs can be made to restore the worn away contact...I recommend beryllium copper for this for it's superior qualities as a spring...soft copper alone probably won't do it for long...I've done this with success...it lasted a loooong time, but now needs it again...

Here's wishing you dry feet!