Yes, there is a 1/4" or so gap caused by the top and bottom black plastic molding on the tank. I first filled the gap with weatherstripping and then silicone after that.
Here's the display tank. A 135G. I bought used for $50. It needed a good cleaning and resiliconing. Dig that 'ol school' corner overflow box!
Here's the sump. It's a 50G. breeder that was cracked on one end. I picked it, and two other tanks, up for power raking a freinds lawn.
and here's a link to a thread that describes how I resiliconed it:
http://www.aquahobby.com/board/viewtopic.php?t=35335
and here's the happy couple.
Here's one of two corner overflows
and a top view
