This happened to me in antiquity, when I was a penniless graduate student. Seems I pulled the knurled hub off of the shaft, put another one over, and ran a small set screw into it to make sure it didn't come off (the wiper arm body keeps the screw from coming out.) It is still in place and working. Can't remember exactly where I got the spare knurled piece-almost seems it came with the wiper arms at the time.