The broken nipple can be easily and properly repaired with the use of a bolt in tire valve stem. Push a wire through the hole all the way to the radiator hose outlet and grab it with pliers to pull out. Put the valve stem over the wire, crimp the wire and then pull the valve stem through until it is in place. Put the rubber washer and nut on the valve stem and tighten down. Leave the valve core out of the valve stem of course. Clamp your hose to the valve stem and you're in business.

I did this to my wifes wagon MANY years ago and it was still going strong many years later when we traded it.