old engineer
I take note of your theory of film loss, and this covers heating of the engine oil. Not enough is being made of high vibration imo, for this is a more damaging way to lose lubricating performance. Though the linear aspect of Ball bearing thrust attenuation here is not usual, I note your confidence in it. A spherical bearing in thrust as here, has two points of contact fore/aft, two per raceway (Four total). Under the load of IPT aft force, a vibration works to squeeze a film to zero, and the phosphating you discuss is left not to lubricate, but armor the Race and the Ball against significant "chatter"? It is not out of the realm of possibilities to suggest that the number of surfaces diminishes as vibration (and imposters, a resonant) can move to unload a number of balls, leaving fewer still to take the load. The Main bearing was reworked due to spalling, what was the remedy? More frequent inspections. Rolls may have been too casual with some results from the test bed prior to introducing this Engine. Too late with the Rumour, but better than never.