Keel Bolt Replacement

I have a swing keel First 24. Have any members any experience of replacing the keel bolts on this model? We had a leak last summer and have concluded that the keel bolts were the only possible cause. I have loosened a couple to get an idea of the setup, however the bolts turn but do not extract. I had rather hoped that they were studded into the keel section but no such luck!
Any suggestions comments would be greatly appreciated.