TrisG
Be assured, the gearbox, like the whole helicopter, is inspected at one level or another, daily. In fact, if you count the HUMS too, almost constantly.
I know there is a lot of discussion going on about how effective HUMS is, and clearly (like everything) the technology still evolves, but in truth it’s a powerful tool which helps engineers monitor the condition of critical components on an ongoing basis and helicopter flight is safer for it.
Next time you land, perhaps ask your helicopter company if they could offer you a few minutes to show you around engineering and tell you how the maintenance plans work. You’ll be comforted, whoever you are flying with.