Looks like original wood to me. A Lang of that vintage and evident quality would not have been let out the door with a stock that had an inclusion in the head of it. keith just wants to disagree with me. Buy the gun, remove the fill and repair it properly and you are good to go.
My thought on this defect was the same as your initial thought Woodreaux... a natural defect in the grain of the wood. My opinion was purely based upon what I see in your photos. My opinion has not changed. I can't help it if Stevies feelings are hurt over that. He's one of those thin-skinned sensitive little flower types.
I'd be interested though, in seeing better photos if and when you buy this gun. And if you do dig out this flaw and find it to be some badly color matched wood filler, it isn't going to hurt my feelings because I was wrong about what I see in a photo. I call 'em as I see 'em, and I'm not perfect.
