Sweating intake manifold gasket.

Did you use sealer around the water jackets? I wouldn't run it till I pulled the intake, inspected it for the possible cause (could be heads or intake have been cut a lot), re-sealed with new gaskets and a RTV around the ports on both sides of the gaskets. Also, I use Indian head Shellac around the intake ports and RTV around the water jackets and china walls (thick bead across the china walls and a heavy dose in all 4 corners)