Hope someone can help. Finally tracked down the oil leak on my 59 GMC with a 270 engine that had baffeled myself and the previous owner. I found a small hole (about 1/16" dia.)in an raised boss on the block just below and toward the rear of the block just below the distributor. It appears to be a hex plug screwed into the block but it has a hole in the center. Stuck a rod in it while engine was running and it touched the camshaft. Does anyone have any idea what this plug or what ever it is might be for. Perhaps an oil return? I cleaned the area and sealed with silicon. Hope my description as adaquate. Thanks 58GMC100