Barry -
Modern synthetic diesel-formulated engine oil is low-SAPS by design, and most ULSD has synthetic additives to boost lubricity, so lubricity and breakdown generally isn't an issue any more like it was back in the day when all we had was good ol' fashioned natural dinosaur juice to run in our "oil burners".
Doing it today in a modern turbodiesel with high-pressure fuel pumps on a common rail with direct injection may also foul the injector system.
Instead, I generally add something like
PowerService DieselKleen maybe once a quarter, or before a long road trip where I know I'll burn through a whole tank in one go. I asked JLR about fuel additives a while back and they said they recommended another brand -
BG DFC - only when absolutely necessary, such as when ULSD wasn't available or if the vehicle has sat for a long time, or for very cold weather anti-gel protection.
In my "cheater" Volkswagen Touareg, I never used any additives other than DieselKleen once in a while and it ran strong for almost 7 years and well over 100,000 miles until Volkswagen paid me a lot of money to take it off my hands.
AdBlue actually has nothing to do with the engine oil - AdBlue is used to catalyze the oxides of nitrogen that are present in higher concentrations in diesel exhaust vs. gas exhaust, and it's injected in the exhaust stream downstream of the EGR return.
