i dont think this type of oil is readily available in the local market yet
i agree that there are other culprits (eg diesel fuel, engine oil additives added to what is already packed in the oil, fuel additives) to consider in the sludge build up on a diesel engine. in order to come up with a conclusive finding one can only engage in the process of elimination by doing away with some items not necessary in the combustion process such as the utilization of additives. that leaves the essentials only like the fuel & engine oil, by using a cleaner fuel like a euro4 type will help isolate the problem whether its the engine oil or not
in all these the original proposition of collecting used oil sample after an oil change & checking what you find in it afterwards still stand