It's possible the leak will self-seal after a few more heat/cool cycles. You could also try a hot retorque, by bringing the engine up to running temp and loosening the head bolts one at a time and retightening while the engine is still hot. Last resort, treat the cooling system with a solution of sodium silicate (water glass) and running the engine for several miles before letting it cool down. That's an old trick we used to use to cure seep leaks after radiator repairs, but it also works on gasket leaks that don't involve sealing compression pressure.
Jerry
