Engine oil level goes down

[Water Warrior 2]

GZ 250.........1-1.5 ml of oil ?? Are you going by the marks on the oil bottle. Each mark is 100 ml. 10 marks would be 1000 ml or 1 liter. If you are adding 100 to 150 mls twice between oil changes that is probably an acceptable amount in my opinion. You must remember that the GZ is air cooled and does not have the close tolerances of a water cooled engine. This is to allow for expansion and contraction of engine parts over a wide range of operating temps. Water cooled engines only get to a predetermined operating temp and are designed with closer tolerances. Some will still use oil regardless of a controlled operating temp.
The bike using a little oil and forcing you to keep an eye on it is probably a good thing. You may spot something else that needs attention.