Through viewing loads of posts here it would appear that the randomly parking wipers feature is a common optional extra on the Mk4, and the only fix is to replace the motor.
Searching the various online scrappies it seems £35-£45 is the going rate for a used one (I've not yet got a price for a new one). Now I don't mind fitting a used one - so long as I can check it is a good one before I donate loads of knuckle skin in changing it! Does anyone know how I can prove I get a good one?
Also, given what a common problem this appears to be, ONE of you resourceful souls will surely have pulled one apart to fix it! I'm thinking that, once I've got my old one on the bench, I might try to fix it (which will give me a spare in case my 'new' one turns out to be crap). Has anyone ever successfully repaired one?