Put the sling in first from the left side, plenty of slack. Put oiler into cutout all the way and push toward sight end of gun. Then take loose end and insert back into cutout. You can kind of wiggle oiler to get a little more clearance, but end of sling will go in. You can get some needle nose pliers or some tweezers to reach back in from the left side to grab it and pull back through. You cannot wrap the oiler with your sling and pull back into the slot, it wont go in. You have to thread it in put the oiler all the way in and thread it back through if that makes sense to you.