Like the others who replied I retightened the nut on the wiper arm shaft to good effect. It has come loose a handful of times over the years on my 850 (1995), when the wipers had heavy use (lots of snow or driving rain). Eventually the splines on the arm and/or shaft wore and tightening no longer worked. I planned to replace the arm, but on a trip, as an expedient, I shimmed the worn space with a little piece (about 3/4 x 1 cm) of waterproof fine sandpaper and tightened it well. It has not come loose in 3 years.