Next time the intake comes off, clean all the old gasket and sealant from everything. Get pictures of how the intake gasket looks on the head and then on the intake.
Place the intake on the heads with NO gaskets, then use feeler gauges at the top and near the bottom of the intake, between the intake and head. This is not precise, but it’s a start. I assume no feeler gauge fits at the top and some thickness will fit at the bottom.