X2 he should have used the cork/rubber end gaskets, the dodge dealer sells ones that have little tabs that you instert into the block and it holds the gaskets they work great then
I have been using rtv on the ends for quite a while when using these manifolds. Before the issue began, I had had the manifold on with the rtv for over 15000 miles. I tried new gaskets and rtv again...no change.
I dont use the end gaskets, as they never seem to prevent the oil leaks.