What the heck is a "heat sink?"
Try a torque wrench on the top end bolts before doing anything else. Several people have reported needing to retorque top end bolts to stop oil leaking. Page 4-62 in the main service manual you can download for free has the correct torques and tightening sequence for the cylinder and head. It's more complex than just the 4 big hex-head bolts on top of the head.