You are right . If he had to add refrigerant then it has a leak ( it does not use it up ) The problem is finding the leak. Many times they are extremely hard to find and newer refrigerators don't require much ( 5 oz.s or so ) so even a slight leak is a major factor in keeping the temp right. Have your tech install a UV filter-drier and put the exact charge in - that way when it gets low again ( and it will ) he can use a U V light and find where it is leaking. Make sure your condensing coil is clean as that will help your fridge run cooler also. Thanks for using justanswer.