[Ray Cox]

Haven’t seen anyone mention it and I assume you already checked but thought I would mention it to be sure.
Did you check the head stud length? With parts quality control these days things happen. Or if the head was decked more.
Make sure when you’re torquing it the nut is not bottoming on the threads before it’s fully tight. We have had some that after decking the heads a lot the stud was a few thousands too long. We added another head stud washer to get the proper torque.

But there are plenty of types of motors that have studs that go through to water jackets. On those type motors they put silicone in the head studs and seal them up. I think it would seal with silicone no issues.