@SASless: the Seahawk/Blackhawk/S-70 main rotor shaft goes all the way through the transmission "box" from the bottom (where the Jesus nut is) out through the top to the head, though the shaft extension is what connects it to the hub. I am pretty sure the S-92 is the same since the gbx (and much else) were S-70/Blackhawk derivative. There are a variety of things that can go badly.
Well over a decade ago a carrier assembly had a serious failure inside a Blackhawk box, which was a major factor in the Navy, the Army (and IIRC the Air Force) getting together with Sikorsky and agreeing on an improvement/redesign of the carrier assembly. So far so good.
Gearboxes are hard things to get right, to be sure. (I think the guys at Sikorsky are reliving that reality again as they work their way through the details on the CH-53K).