Sergei, be very careful.
You will need information, probably from Nauticat, as to exactly what kind of bolts they are. What material, size, torque, and how they are fixed, are they Thru-bolts, cast in, tapped in from above etc…..
Your description of ‘crack’ is not clear, is it in the bedding compound between the lead and the fibreglass hull ? It may appear as a crack but might be sound but in need of re-filling. Fin keels occasionally fall off when bolts break due to unreported / checked collision damage incurred when a keel has hit an underwater object. This may have happened years before as in the old Beneteau which capsized in the Atlantic a few years ago.
This is a professional job for a boatyard, good luck.
Ned Coackley N33 521