On vintage military bolt action rifles, we relieve the stock area around the receiver tang of wood to prevent cracks like that. Not sure you could do that in this case. A lot of guys use super glue (cyanoacrylate) to repair splits as it flows deeply into splits/cracks. I've never personally tried it. If that is a crack, it likely needs to be isolated and repaired due to its location. Just my 2 cents...