Hopefully, as has been mentioned earlier, it could just be a gasket. This is not unusual on these engines. As Dave says, be mindful with the material choice for studs etc. Aluminium is particular susceptible to electrolytic action from dissimilar metals.
I remember when manifold nuts were made of copper. Never got the problems we get now as it was sacrificial so as long as you used the correct tight fitting tools, all it done if it did not want to come off was strip the thread in the nut. At least that left the stud where it was with out shearing it off in the head which is a right nightmare.
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