Hemi, yes that was what caused your leak.
Diablo, a heavy sleeve should fix it, but also keeping the oring out in to where I put the big bore oring will also. I have since changed how I do all stock heads to miss this spot. Cool heads standard domes force you to place the oring groove rite over the liner and cylinder interface, so a standard cool head can cause issues be sure to look carefully at cylinder deck before oringing. I have seen this gap from a few thousandths to a milimeter wide and up to 3 mm deep