Hi Folks
While performing a minor valve job we discovered cracks in the seats of 3 intake valves . The pic is typical of all three. My machinist said he can replace the seat but feels the crack is in the head as well.
Cast iron Indy 440-1c .

Why did this happen?

Has anyone had any luck repairing this ?

Does anyone know the depth of the original valve seat on this head

Thanks for looking