we had used a sealant in the water & the mark the sealant left at the gasket edge was a real rigid line, no chance of it leaking past the Cometic gasket. especially with the nice imprint the copper coat left on the faces with these gaskets, this motor didn't even leave the workshop after we had planned the head & had done tests. the water leak was sizable, not just a little weep. i'm a Cometic gasket veteran, with my Indy motor used 1 set of gaskets 9 times before we developed a leak, i'm good at looking at these parts.