Anybody have this problem with their wipers? The wiper arms keep coming loose at the most inopportune times,like when I'm using them. I have to tighten them up with those wrenches that Volvo supplies at least once every two months. I was wondering if there is supposed to be a lock washer under the nut on the the shaft that holds the arm. I don't have one on mine. Should I put one on or try some Lock-Tite to keep them in place?

Thanks
Neil