The buttstock is 80 years old but in excellent shape, notwithstanding the wrist crack. I carried the gun turkey hunting for several years with a slip on type sling, and one morning it slipped off, hit a hard surface (of course it wouldn't slip off while I'm marching through the swamp). The crack is unnoticeable unless force is applied, and then it only opens slightly. A very thin glue might seep in, any suggestions as to what I might use?