i have just encountered the problem, when you open up the plastic covers and remove the, windscreen wipers the motor is visible, there are four plastic clips which hold on the electrical part of the motor, when i took it off there was burn marks on the copper wiring to the earth, the copper was snapped in half but the fuse hadnt blown, not sure what that means, but im sure its because it is not earthed properly, i have ordered a new part from a breakers for 100euros as i live in finand, maybe you can search for breakers in your area, hope this helps.
Matt Jordan, August 2009