I had the same issue and had the reusable gaskets with the steel core. Did you use gasket sealer on the gaskets? I didn't and when I did the leak is now gone.
I decided this had to be the case as well, since I sealed around all the ports but not the bolt holes. (just the bolt threads)
If the threads are sealed it HAS to come up around the bolts and not up through the threads.
And the only place it can do that is by getting past the gasket.