Loctite 420 is extremely thin, a lot goes a long way, or all over your bow when it runs. Use 400 grit emery paper to roughen the scratch/crack and use one drop and a toothpick to spread it in the crack. After it dries you can sand lightly with 150, 200, 400, 600 etc. remove dust and spread a little True Oil over it. When dry hand spread a thin 2 coat. Repeat up to 6 coats or whatever your happy with. Use rubber gloves, and work over a safe protected area. It likes to run everywhere.
Put the top on the Loctite, tape it, put it in a plastic zip lock bag and in the refrig. or it will eventually dry out. Loctite 420 is a bit expensive, $20 +.