Intake Manifold leaks Coolant- Could it be too small??

Dunno if this helps but I usually run a big bead of silicone on the ends in place of the manifold end gaskets on the block then torque to spec. I would think the aluminum would seal if the water jacket ends are flat. Maybe try run silicone around the water ports with the gasket that sits between the heads and manifold...

what you don't want is antifreeze leaking into lifter valley into oil etc. Good luck.