My experience agrees with the above and I would add that today, there are alloy welding rods that allow "cold" welding of cast iron. As above, I don't intend to start a fool flame war, but will add that even with the alloy rod, welding cast iron is not a job for the occasional welder, which includes most automotive machine shops. There are facilities which specialize in this type of work, with engine blociks being only part of their work.
Another alternative is "pinning" the crack. Most any quality automotive machine shop can do this. Is simply stopping the crack from getting longer, by drilling a hole at each end of the crack and inserting a steel pin. Location of the crack dictates whether it is feasible or not.
Although mentioned above, a sleeve was used to contain
oil flow, what was not done, or at least mentioned, was stopping the crack from growing, which I guarantee will happen, especially in a mechanically stressed area of the block.
My suggestion is to have a facility specializing in repair of this type having a look at the block.
Al