The wiper arms are made from cheap, possibly white metal. There are splines on both the arm and the wiper shaft, clean out the grooves on the shaft , get a hacksaw blade, grind it so it fits in the wiper arm hole and cut some new splines in there. It won't last forever, but should keep you going until you buy new or good used. Be careful because if you do cheap out ,they will fail at the worse time- during a big downpour.