How come I get oil leaks at the corners of my intake manifold?
Most rebuilt engines have been machined in one way or another. Two of these places are the block's deck surface and the other is the head surface. Every time material is removed from these two spots by "decking the block" or "surfacing the heads", the intake manifold sits higher on the block simply because you have "lowered" the heads by machining the surfaces. When you try to stuff those rubber or cork end seals underneath your intake manifold, it causes the manifold to ride even higher and you either need real thick intake manifold gaskets or you need to have your intake manifold end surfaces machined down a bit. The easiest way is to throw out those end seals and just use a bead of silicone. The oil in the lifter valley is just splash and not under pressure. Another big problem you run into when trying to use those end seals are vacuum leaks underneath the intake manifold. It's best to just not use those seals in the first place and go with the silicone instead.