The 6.0 block has two sections, the upper section,which is the main meat of the block and a lower section (the bedplate) that acts as the bottom end of the engine. this is a one piece section that has the main caps integrated into it for strength. there is a gasket between these two sections of block and it is called the bedplate gasket. I kind of doubt that is the source of your leak based on what you describe, but could be wrong.