Hmmm, i would question the duty cycle that the gearbox was undergoing. I imagine that Police choppers will do a lot more agressive manouvreing that most choppers. This means the mast thrust bearings and tail rotor output bearings will be seeing more load. Worrying when you consider rotor component fatigue lifes.
I can't imagine the power input being a problem, unless the engine is normally derated but has been increased for Police usage. It is possible they are using oil, which while being in spec, is not as durable thus reducing bearing life.
Really, i would need to know more about the actual nature of the failures to do anything more than speculate.
Mart