It is possible that there was some junk in the bottom of a bolt hole that when the header bolt was screwed in punched a hole through to the water jacket. I have seen this happen so many times its disgusting. Takes a minute to clean out bolt holes with a tap or high pressure jet, even poking a pick in there will get it and yet people keep doing it. The give away is that the bolt was tightened to stop the leak. If the bolt had bottomed out the extra torque pushed something somewhere. )added) sorry I went on a rant. Pull the header bolts one at a time if you strike water you've found the problem. I don't think D4 Hemi heads have bolts into the water jackets.