On-wing repair
Not sure of all the implicatios here, but field on-wing repair of this GE90 night have been feasible given one or two bits of data.
The loss of gearbox drive power might have been diagnosed with a simple cranking check; the N2 sensor on the mainshaft, fwd compressor bearing area would show no response to gearbox rotation. No mechanical connection. It's either the angle gearbox, or the input or output shafting.
I've done this in the test cell, but not on-wing, and certainly not in the Arctic!