I'm sure I've written this before but will do so again. From the Canadian 1943 "Extracts From Instructions for Armourers"
NOTE, - A split at the rear end of the fore-end, at the junction portion under the stock bolt plate, may be ignored, provided the screwed wire has a firm hold.
That being the word from the experts, I'd also degrease it as best I could and work some good quality wood glue into the crack and clamp it up overnight with a C-clamp padded with leather. It may just crack again but it certainly can't hurt.