Im pretty sure, when my block we bored out, or even way back when it was poured into the mold. it was given a special treatment that gave it a cheese cloth type structure, for oil to poor out constantly.
my car has sat for a year... and there is fresh oil around the valve cover, from where... who knows. i swear there are mitsubishi pixies or midgets or something that get in and poor oil all over the engine.... lol