Rather than oil used / kms.
A general rule of thumb 0.5% oil consumption per litre of fuel used is starting to be excessive on diesel engines (This is not a Fuso spec)
All engines should use some oil, as oil will get caught in the honing marks on the cylinder wall.
If the engine is not using oil this can be caused by the oil temperature is not getting up to a high enough temp to flash off any condensation.
An example that can happen is that if the engine has done say 4000kms around town, you check the oil all is ok, then you head off & do 1000kms in a day You may find that it has used 1 to 2 lts in the day, this is not excessive, as the engine has flashed off the condensation which has been replacing the oil that was burnt during the 1st 4000km of operation.
For information, 2002 NPS300 Naturally Aspirated 170000kms
I just recently did a trip from Cairns - Windsor NSW - Cairns, fully loaded + towing a Duel axle trailer with 1800kg Boat (Nothing was above the hight of the Cab). Road speed between 80 - 95km/h. Distance Travelled 5700 kms - Fuel Used 1036lts. Oil Consumed 2.3 lts