The oil coking problem in pipes was detected and explained on some earlier incidents with other type Trent engines. The pipes involved where bearing chamber vent pipes. It was anticipated in investigation that the coking blocked these pipes leading to heating and failure of the bearings.
It was also in the first segment of this thread once mentioned in conection with the QF 32 engine failure. I didnīt even know that oil coking could become a cause of problems in bearings. But I can see your point.