Gary wyborn

We have a 2012 Landcrusier 200 series diesel and tow an off road van 3.5 ton with it , this last trip it used nearly a litre of oil over 4000km … it did this 2 years ago and has not done it again until now … both times it did this it was tough hilly terrain . Is this normal or should I be concerned .. always regularly serviced etc has 200,000 kms on it …