Tried your suggestion. Can't lift plastic cover (as you would on ordinary wiper). Managed to move the rubber grommet (between body and wiper) out of the way and all there is is something that looks like a collar (which looks as though it's split a little) but no nut to undo, also there would be no way to lift it off cos tube to washer (which is built in to cover) has no spare length. Any more suggestions. Wish I could get a book for the damned thing.