The blades on my DSY4500 were not cutting evenly. I had a Craftsman tech check it out and he said that I must have hit something pretty hard. One of my blades was badly bent and the mandrel shaft stars were badly worn. He suggested I replace the blade and the mandrel shaft. He advised the replacement of the mandrel shaft would run close to $500. Is this something that the average guy might be able to replace to save some money or should I leave this one to the experts?