You are going to have what is called dead space using this type of system unless you purchase a low dead space syringe or use insulin needles. While the syringe does account for the dead space, and you are receiving your correct dose, as you have seen there is about .10mL being wasted. Even if you were to draw up .10mL of air and get it to the top of the syringe near the plunger and inject it after the oil to clear the needle and hub (which would be fine to do), you still would be "wasting" because you would be using over your prescribed dose.
You could draw up .10 or .07 less than you are prescribed, pull up the plunger to clear the 18g needle of contents (this is the oil that you are wasting) which will bring the amount of oil to your prescribed dose in the syringe and then pull .10mL of air into the syringe and get the bubble near the plunger. Then change to the other gauge you are using and push the oil down the new needle until you see a drop and then inject, allowing the bubble at the end to clear the dead space and thus giving you your full dosage with little waste and without going over your prescribed dose.