Details about the chopper loading and Osprey problems
Many of the choppers were built in the 60's. For a while there just were no spare parts. The CH-46 was restricted to a light load, as you said, because if anything broke it was out of service. They started cannibalizing one to keep another flying. Rotor hubs showed fine stress fractures on many/most of them. I believe a couple of years ago they did finally get authorization to make some more roter hubs and blades.
The problem with the Osprey, if I'm thinking about the same one as you, is related to the extreme diameter of the rotors and the aerodynamic effect of sharp turns while descending. Basically, the inboard rotor "stands still" while the plane executes a sharp turn around it, while the outboard rotor gains speed. With a single rotor there is no separation to induce the differential lift, and on the Harrier the thrust is not dependant on a horizontal rotation. The differential is not huge, but it's enough to increase the rate of roll -- a nasty feedback loop.
