Hi Mudplug, The wiper motor has a metal "park" track inside on the plastic gear wheel which allows the motor to continue to run until it gets to it's rest position - it stops when the motor (small contact inside) passes the end of the "park" track. This is used for intermittent wipe (CCU pushes wiper off rest and motor runs via "park" track) and also when you manually blip the stalk for a single wipe. If only this function stops working then the motor track is FUBAR'D - you can take the top off and look for the worn contact - a simple repair.
Otherwise a replacement is your option - as said above a simple circuit no complex electickery in the wipers.
Can most-times be fixed by a simple bend of the contact spring or extending the worn contact with a small bit of brass strip or flattened copper wire if you can solder?