These keel bolts are very bad and the boat is in danger of capsizing when the keel falls off. There are several ways of repairing the keel bolts. The first is to take the keel of and melt out the old keel bolt and weld the lead around a new keel bolts. This is kind of expensive but about 300 per bolt.
The way my company does it is to drill and tap in new keel bolts. This cost about 300 per bolt and does not require the keel to be taken off. This way if done by a company called Keel bolt Inspection and Repair can be done on most keels.
If you can't afford to have it done then you can pocket in the bolts your self. Use 316 Stainless steel all thread material and drill down into the lead with 1/2 " drills and work your way up to the bolt dia