I've fixed my rain sensor wipers (for now at least). The rain sensor would work fine for a while but the wipers would stop at random positions and sometimes the system would go to sleep completely. Resetting the system (wiper off then on again) allowed the system to work again but only for a few moments.
To fix the problem:
Remove the wiper linkage and motor assembly.
Remove the wiper motor from the linkage.
Remove the black control box from the wiper motor - it's held on by plastic clips.
Attached to the control unit, are three copper brushes. The brushes pass through slots in a plate so that they contact a segmented metal disc on the worm wheel. The disc gets contaminated with grease from the worm and worm wheel and the resulting bad contact causes the silly behaviour.
Unfortunately the worm wheel is hidden beneath a slotted plate so it's very difficult to clean. The plate is riveted onto the gear housing.
I filed the rivet heads off so that the plate could be removed and the segmented disc could be cleaned up (I also cleaned the copper brushes).
I drilled out the rivets and tapped the holes (2.5mm drill, M3 tap) and re fitted the plate with M3 screws.
Great success - wipers work properly
