No it's is very likely to leak and cork is clearly the culprit. Cork
gaskets are not made of solid cork but particles glued together. The hole
is stopped by the cork or rubber gasket. True, it can't blow out because
the gasket is backed up by the solid metal of the pump flange. What almost
certainly happens is that oil works it's way between the cork particles and
makes a small crack. It may even have an effect on the glue holding the
gasket together. The hydraulic pressure pushes the gasket both ways. Any
oil that then gets through to the interface between the metal and the gasket
lubes the sliding surface. The gasket blows out sideways and the oil blows
out of the engine.

It's not so much that the rubber is stronger or a better gasket overall but
that it is less likely to separate and let oil and pressure into the gasket
itself. Putting pressure on a gasket in this way is rather unusual and cork
gaskets have all the characteristics that would make them failure prone even
though perfectly adequate in other situations.
--
Roger Long
It really doesn't matter. On the dry pump, there's solid metal on the
other
side of that hole. There's no way it's gonna leak.

George Patterson
Brute force has an elegance all its own.