About the only way I know of to crack an injector body is to over tighten the two screws, or not have the piece of tube that goes on the one screw as a spacer. That's unless the brine valve cracked it somehow.
Now you should inspect the orings on the brine valve, it may be allowing a leak to the brine tank during service. You may have one on wrong or damaged.
You'd have to look at the flow diagram to see if the seals and piston could cause it; I'm unsure if they would.