The toilet needs to be replaced. This is not something you want to mess around with. It’s a matter of when your toilet is going to fail rather than if it will fail. The cost to replace a toilet is a few hundred dollars for the toilet and an hour or two of a plumbers time. When the cracked toilet fails it can lead to damage to your bathroom and other rooms in your house which could cost much more and your still paying for the replacement toilet and plumbers time.