If the cracked wood surfaces contain oil or grease, the glue will not adhere properly for a premanent bond. Make sure those surfaces are properly degreased first; even better, have a pro fix the cracks and there is a good possibility the repair can be made invisible. Glues that do not properly bond will still often stain/seal the ends of the wood grain so that any future wood repair, even when properly done, will result in the repair being visible. As FYI, those cracks are probably the result of someone trying to force the forearm in place with hammers in the fired position; a no no for a Smith gun (never remove a Smith forearm with the gun in the fired position).