Bearfoil
I am with you on this. I think that shaft coupling spline wear on engines with such limited hours and cycles is very unusual. Splines are coated with wear resistant coatings to prevent premature wear. Today's modern high-bypass fan engines are designed to stay on wing for many cycles and hours before removal, teardown, inspection and component repair or replacement. Some stay on wing for as long as five years of operation accumulating many cycles quickly (shorter routes). Spline wear is not a problem that you normally think of or worry about. Engines are generally removed because of a deteriorating EGT margin. This is generally due to hot section degradation, particularly the combustor and turbine rotor blade tip seals. Obviously operating conditions and individual operators have a lot to do with on wing engine life.
This spline situation on the 900 is very odd indeed. Just some thoughts.
Turbine D