Smile!, youre not alone i liked the Axor too. Mercs come without a dipstick-alas. For now wait until the computer asks for oil. It should reccomend you put 5 litres in,put in 4 
If this doesnt suit you open the grill and as you look at it to the right of the rad. you will see a dipstick sleeve with a cap on it. Be careful removing the cap as there is a rubber washer there that you will need.
Then go in to the dealers and tell them the truck is saying both too much or too little oil. They will want to check the sensor but insist you want a dipstick. Tell them if anything goes wrong you asked them for a poxy dipstick and they said no.
At this point they will give you a dipstick f.o.c.