Macbow took the words out of my mouth. I've had good luck with super glue (cyanoacrylate), fixing splinters or small cracks, I think the key is catching them early. Have used it in pin knots as well, and they have held up. For the sinew wrap, you could also try 2 ton Epoxy, That has worked well for me where penetration isn't needed. But for cracks let the super glue saturated and seep in, dry, then apply more until it is full, then sand with ascending grits, and it looks great.