Mike, there is a product called "Irontite". Sold at "Car Quest" auto parts stores. It's a liquid, 16 oz. bottle.
I have used this product many times on blown head gaskets were motor anti-freeze is leaking either inside the motor or outside of the head.
Make sure engine is warm (not hot), open rad cap if you got one and pour it all in. Make sure you got enough room for the entire bottle. Run for 5 minutes. After that time you will know if it works on your particular problem.
Make sure your heater is turned off first.