You know, sometimes I take things for granted, and I might have overlooked an important point:
FE intake gaskest should be metal (steel core laminate) and not plain gasket material. There is much discussion around the net about using correct gaskets, and warnings about using certain Fel-Pro gaskets.
These manifolds tend to make the gasket squirm as they are tightened. We covered that part, but I failed to warn against using Fel-Pro Print-O-Seal gaskets. They squirm and they leak.
Not all Fel-Pro gaskets are created equal. Fel-Pro Q1247S3 gasket is a good one because it does have a steel core.
Other brands are good too like Victor Reinz Nitroseal intake gaskets:
95186SG 1.20" x 2.00" Large coolant
95187SG 1.20" x 2.00" Small coolant
95197SG 1.28" x 2.10" Small coolant
Ford Racing and Edelbrock also have good gaskets. Hope this helps. - Dave