there`s an active thread on XT-660.de regarding this problem.
It seems, that Z - swingarms left factory without any grease.

foto: http://www.bilder-upload.eu/show.php...DE6A5DjnHI.JPG

The chances are youve washed all the lube from the bearings, thats why it stopped with some wd40, you should remove um n pack um with some grease .
and from now on when you jet wash your bike avoid wheel hubs, shock linkages and the headstock and not to mention the electrics.