Hi,
It sounds like a spoke has been over tightened in the past, I would replace the hub.
If I couldn't get a replacement, I would strip it out and carefully, check it for other cracks (using penetrant spray or magnetic crack detection). You've probably heard of wheeltappers, tapping/ringing the hub when it's stripped down will give you a good indication of its health.
If I was confident it was safe to use after a repair, I would drill a small hole at the end of the crack to stop it migrating. Braze and lightly tighten the spoke, as one spoke left like that would be okay but I would monitor regularly.
Best of luck...........