Windshield Wiper Fluid Levels

So… I noticed that the windshield wiper fluid in the neck of my reservoir kept going down. I took the vehicle to the dealer who inspected it and determined that it was a bad gasket between the upper and lower reservoirs so they decided to replace it. Everything was fine on my ride home from the repair and even after a few days of sitting. But then I decided to take it out today and checked the levels after driving for a while. Surprise, the level of the fluid went down. Not by much but still went down.
Could this be from the cold nights?
Could this have been from an air pocket?
Could it still have a leak?

Thanks!