If you are referring to the leak stop radiator stuff--which I think is the same stuff, yes I have. My wife's car had a leak at the head gasket of which the mechanic told us the gasket would blow by the end of summer--2 months later. I put the stop leak into the radiator on the chance that it might help--cheaper than the cost of a new head gasket. Low and behold, it worked like a charm. It has been 3 years now on that same engine and no problems. No leaks. The stuff works and its cheap.

I hope this helps. Good luck. Might it be possible that one of the hoses has a small pin hole leak?