Does the Gasgacinch need to go on both sides of the lower gasket coolant ports?IS THE MANIFOLD BASE GASKET SURFACE FLAT? Multiple leakages makes me suspect that the manifold is warped, even if it isn't pitted. It may be both warped AND pitted. Plane the manifold, which will remove some or all of the pitting. If there's pitting remaining after it's been shaved, fill the pits in with epoxy as stated earlier.
Depending on how much material is removed from the manifold, you may/may not have to use thicker manifold gaskets to take up the extra room. (Probably not.)
The rubber end-seals on the "China Walls" can be entirely replaced with QUALITY RTV Silicone. When it's me, the O-N-L-Y stuff I'll use there is Permatex The Right Stuff. When the rubber seals are replaced by RTV Silicone, there's no stress on the manifold pushing "up" as the manifold bolts are tightened.
Fel-Pro claims that their gaskets need no gasket sealer...but I still want to stick the gaskets to the cylinder head with Gasgacinch or some other gasket sealer. RTV Silicone is not a gasket sealer. It's used INSTEAD of a gasket (or rubber seal), not applied TO a gasket.