Power steering box leaking oil.

Do you mean the power steering pump?

Leaking seal and worn part required a pump overhaul or replacement. They are usually replaced. However, many times leaking pump can be resealed if an overhaul is elected. Consult the factory manual first for details and proper procedures.
After a repair has been made to the power steering system, bleeding will be necessary to remove trapped air and to obtain a correct fluid level. Refere to the factory manual for bleeding procedures on the specific vehicle being serviced.