It probably is a duck(*)
Per AD:
Wear, beyond Engine Manual limits, has been identified on the abutment
faces of the splines on the Trent 900 Intermediate Pressure (IP) shaft rigid
coupling on several engines during strip. The shaft to coupling spline
interface provides the means of controlling the turbine axial setting and
wear through of the splines would permit the IP turbine to move
rearwards. Rearward movement of the IP turbine would enable contact with static turbine components and would result in loss of engine performance with
potential for in-flight shut down, oil migration and oil fire below the LP
turbine discs prior to sufficient indication resulting in loss of LP turbine disc
integrity. Some of these conditions present a potential unsafe condition to
the aeroplane.
Compliance Time: Engines where the life since new is 250 flight cycles or less (1) Before the engine has accumulated 400 flight cycles since new.
* Duck in this case being a design fault.
HCD