The MLS gaskets are coated. The chemical reaction between dissimilar metals is called "Galvanic corrosion". The small holes/slots restricting coolant flow are by design. The coolant is supposed to flow from the front of the block to the rear of the block, up through the big hole at the rear of the cylinder head then to the front of the cylinder head. The restrictions in the gasket help force the coolant to the rear of the block, but also allow some cooler coolant up to the head to equalize the themperatures through the cylinder head.
