There's an old saying; 'If it ain't broke don't fix it.'
This gearbox design has been going since 1966 and over the years, 1971 to 2008 in my case, and it has performed flawlessly. It wsn't until it entered civil service in the mid seventies that a gearbox oil pressure guage was even fitted; before that it was just an MgpP warning. The obvious structural difference between the two is that on the old ones the pump was mounted on the back with the alternators and hydraulics as the shaft had to be kept hollow for gunsights etc. I can understand using the shaft as an alternative drive for a standby system but why the main one as well? and if it did work why change the material.
Another example of this saying was with the BV 234 Chinook. They had millions of hours being beaten to death in Viet Nam without any trouble; the North Sea was going to be a walk in the park. For some reason they decided to make the front gearbox bevel gear in two pieces; possibly so that only the wearing surface needed to be replaced at the TBO. What they did not expect was corrosion to fracture the coupling between them and cause the gear to fail and cause the disaster at Sumburgh.
One must wonder how many problems are caused by nothing more than change for the sake of change.