squib66,
As you note, the 53K aux. lube circuits are used in the MRGB, input nose GB's, and IGB/TRGB's. The aux. lube systems use a supplementary oil volume that is "misted" onto critical gear meshes and bearing using bleed air pressure from the ECS. The critical gear meshes tend to be the spiral bevels used in the nose input GB's, the IGB and the TRGB.
I believe the 53K MRGB also has switched to an aluminum housing material, since there were significant maintenance costs associated with the mag housings on the 53E's.
Lastly, the FRA MMC material you referenced from Triton is pretty neat stuff. It is used for rolling element bearing liners in mag or aluminum housings. On a big MRGB housing like the 53K's, it can probably save about 50 lbs versus carburized steel liners. But at about $300/lb, it is definitely not cheap!
riff_raff