Intake manifold advice for a 100% no leaker. Do away with the front and rear gasket on the intake manifold. When you reset the intake manifold, use the intake to head gasket. For the front and rear, use a 3/8" bead of silicone sealer. Then set the intake into place. After the silicone has set, you can cut it smooth with a razor blade for a neat look, or leave as is.
I just did an intake on my buddy's 1971 Jimmy. My procedure was to Gasgacinch the head and the intake gasket. Then I put a small wipe of silicone around the water port. Before setting the gasket in place, I put a small dab of silicone at the corner where the head meets the block. I then set the gasket on the head, after the Gasgacinch becomes tacky. Then I set a thin wipe of silicone, again, around the water ports, on the gasket itself. A 3/8" bead of silicone front and rear mating surface, then set the manifold onto the valley. Follow the torque sequence first snugging the bolts by hand. Ultimately the torque is 25 ft. lbs. So I take then to ten, then twenty, then twenty five. Then go over them again. Of the dozen or so intakes I have done, nary a leaker in the bunch. And some of those were fleet vehicles that got a lot of mileage and abuse!
