When a critical repair is delegated to others, no matter the provenance, two things:
Responsibility cannot be shrugged off, and a follow on is required for many reasons. It is not so simple as you say. Suffice to say Airbus was obviously satisfied with the protocol for replacement, and they should have been more careful.
Having identified the problem, it is not possible for Airbus to absolve responsibility for its mitigation, as we will see.
Thanks for your time and patience.