There is an 1/8inch plug that seals the hole where they drilled the block. Its behind the side oil cover about an inch down from the lip. If you find the galley cast into the block that goes up to the head you'll see it. You might want to take that off and poke some wire around to see if anything comes up. Its also possible that the plug might be in to far. A very small chance.
Without taking things apart there is no real way to get to that galley. But since there are two 90degree bends at that plug, if sludge is going to settle, that's where it will do it.
