No, but I've got a pretty good idea of what will be going on.
The unit needs to know where the window wiper arm is so that it knows when to stop. Inside the box there is probably a thing called a rotary encoder which is basically brass segments in as circle and a wiper that runs over them. They're often used in volume controls. As the window wiper can sit idle for ages, the copper track can corrode a bit and the wiper arm doesn't make good contact with it. This can throw out the signal so that the box looses track of where the arm is or even gets no signal at all.
If you leave the window wiper running it will rub the brass track clean and start to work ok again. It's that simple.
