NQ,
Appears like a Putty repair between the Oiler slot and Butt plate.
You could use a Paint Pen/Marker to color it over for a better color match.

From your pictures the Sling Webbing looks legit as far as I can see.
Is the sling a D tip or C tip ?
Real C tips are running at and over $100.
Thought being, since your carbine has late features, I'd see no problem with a real post war D tip sling.
Money saved for ammo or to start buying needed tools..... like Bolt tool..etc