CEFOSKEY,
I find the explanation of "metal flaking" in the X2 MRGB quite reasonable. This "metal flaking" is most likely due to case spalls on the bearing races or gears. It is typically a fairly benign failure mode that is easily picked up by the lube system chip detectors. And if you're going to have a drivetrain failure, this is the type to have.
In the particular case of the X2 MRGB, I would speculate that the metal flaking is probably from the final stage gears. The reason I say this is that the X2 appears to have a fairly rigid rotor system with high mast moments. It is very difficult to isolate the MRGB output gear meshes (usually a planetary gearset) from these high mast moments, which tend to cause misalignment at the gear mesh points. The misaligned planet gear meshes tend to edge load and/or not load share properly, which in turn leads to excessive tooth contact stress levels and premature failures like case spalls or pitting.
Designing a lightweight transmission for use with a rigid rotor system is a very difficult engineering task. Sikorsky's drivetrain group definitely has their work cut out for them. I'm sure more drivetrain problems will continue to pop up as they push the performance of this aircraft. It's just the nature of the business.
riff_raff