I always thought that dealerships saved all the castings (like water pumps, brake calipers, etc.) they took off of serviced vehicles and returned them to the car manufacturer for a few dollars each to become the rebuilt units we buy at the auto stores. When I worked at Ford I remember we had a station for rebuilding water pumps. Recently I had my car serviced and I asked the service manager to save the old master cylinder. He told me "Oops, it got thrown in the trash".