I would walk away. I had just this problem with a Jeanneau Sunfast 32. The repairs to the cracks were visible before I bought the boat and I later discovered that this had weakened the attachment of the keel which had to be removed. Everything had to be rebuilt and it cost me a fortune. I also took legal proceedings against the yard that sold me the boat but only got a small proportion of my loss back.
Get out whilst you can!