Thanks for your replies, Superdav95, Jawge and Bjrogg. Sounds promising, or hopeful at least..
I strung the bow so the crack would open up a bit (it is really tight), poured on some superglue which to my surprise did seep in, then quickly restrung it and wrapped a bit. I let it rest for a couple of hours and the crack does seem closed now when I string the bow.
So far so good, but there are more dark growth rings in other places where I suspect more small cracks might appear later on. Guess I have to look for better quality yew next time..