I have seen this type of cracking. It is probably thermal fatigue and can be removed and weld repaired. Based on your photo this is indeed repairablew and does not require replacement.
Balancing? I believe this is a stationary component in a steam turbine. Agree, any weld repairs should be performed by a reputable large steam turbine repair shop.
Based on your drawing, this nozzle assy looks to be a weldment. And the cracks appear to be in one of the weld zones (specifically, right where the drawing specifies "R16"). Is this correct?