When you said "Sleeve," I took that to mean the cylinder bore had been Sleeved. The cylinder bores in the picture do not look like they have been Sleeved.
What I see in the picture is that the
oil gallery coming up to the valve train has been restricted. Typically they tap that hole. Then bore a hole through a plug, and screw the plug in. Your block appears to have a pressed in restrictor. It is fine that it is recessed.
There are four of these
oil holes. Notice the water jacket to the right of the head bolt. Put a straight edge from the
oil hole to the water jacket and make sure the deck is flat. Also look for a crack in the block between the head bolt and the water jacket. The deck can be crack free and the crack be down in the hole. I would try pressurizing the head bolt whole with a compressed air rubber tipped nozzle.