Yes, killed it's use stone dead in the North Sea ISTR. Amazing that anyone survived the crash.
The report doesn't indicate the existence of a 'Military Gearbox', only different modification standards, the change to -6 being the important one in the accident report.
Assumption that modifying the nature of the mating surfaces would not change wear patterns at those surfaces was an error. Underestimation of the acceleration of corrosion due to salt laden air was also a big factor it seems.
Much like the Super Puma, this was the last straw after a number of incidents (including ditchings) and a general dislike of travelling in it.
It was the direct catalyst for the development of HUMS, sponsored by Shell (the client), Bristow and Plessey