No, the head oils through the pushrod not the head. The left lifter galley is fed from the #1 main bearing. A couple things come to mind, you can check them in any order you see fit. First is maybe a spun #1 main bearing, but that would soon wipe out #1 rod bearing as well. Next would be the soft plug behind the cam retainer plate. It may be non existant or could possibly be pressed in to far blocking the feed hole to the lifter galley. Then of course there is the plug at the back of the left galley inside the valley but you said you already checked that.