See if you can dig up something on a Shell turbine oil called ASTO 560.
This oil coked up another RR Trent around 2002.
see:
http://www.ntsb.gov/ntsb/brief2.asp?ev_id=20040528X00693&ntsbno=DCA04IA002&akey=1
It was withdrawn by RR. the oil that is..
I checked and this oil is still widely available, maybe Qantas are still using it. Who knows?
Anyway the bottom line is it was coking the vent tubes from the bearing.