When I find cracks in the wood, I will usually stabilize it with some thin super glue. A lot of the times, as you turn the call down to size, the crack will either disappear or become much smaller. If it hasn't gone away, I'll continue filling it with the super glue. If the crack is still quite large, you can use epoxy mixed with brass filings, crushed stone, saw dust, etc. to fill the gap. Just be creative.
Paul