Lets see now..........................
A bit of history - The 600N wasn't "designed" it just grew from somewhere.
from Uncle Toms Cabin - like Topsy "I wasn't born, I just growed"
Subsequent to that a lot of it doesn't work very well as the original design struggles to keep up with the growth.
To establish where the weak points are from this growth you only need to look at the published data from MDH and go from there.
Finite component lives for example -
Upper Thrust Bearing - 600 hours
Tailboom attach bolts - 300 hours (cracked fittings where the boom has departed)
Collective Stick Housing - 450
Collective Pitch Control Tube - 400
Collective Pitch (Pilot) Tube Assembly - 600
Landing Gear Strut - 696
Some of it is good and that stuff trickled back down into the smaller models (i.e. Main Gearbox)
But most of it was plain awful. If you stand back and look at it the helicopter doesn't have a "big enough" rotor for its size.
Just throwing an extra blade at isn't that simple. There is a lot of drag in the MR for not enough thrust and the pitch angle on the
blades when the required thrust is produced is not optimal. We are dealing with the same blade profile as the 300 remember.
That would also explain amongst other things such as blanketing by the cabin why it Autos like a greased brick at 80 knots.
To explain where I am coming from, I cut my teeth as a mechanic on 500/500C then the introduction of the D/E and put the second
600N ever into service as well as having to fly the thing. It took years off my life and it was during a period of turmoil in the life of MD.
The thing had "Boeing" written on the door.
As they say - Try as you might you can't polish a turd.
shoulda coulda woulda - but still not a solution.