I recently had this really weird "leaking" issue with my 180. There was a super slow water droplet that would form at one particular point in my upper frame. Check the glass and there was no crack. The really weird part was that the water level is always kept about 2" below the upper frame. It did this for a few weeks, then just stopped. I'm theorizing that perhaps it was condensation building up inside the frame channel (where the frame rests on top of the glass), and just got to the point where it got heavy enough and ran down the glass. I bought the tank, used, in 2013 and it was in pretty bad shape, so I stripped and resiliconed the inside, but I didn't reseal where the upper frame portion. This probably is where the humidity is creeping in and building up moisture.