Center overflow water tight?

[Elo500]

Bought a used 120g with center overflow. Some of the silicone that holds it to the glass is gone so that water could enter from the side. Should I add new silicone to make sure water only enters from the top? Or does it not matter?

[thegrun]

If it leaks it will allow more water to flow down into your sump when the return pump is off. When the overflow is watertight the DT water level will drop to the bottom of the teeth of the overflow (assuming you have a anti-siphon hole on the return discharge). If you have a leak in the overflow box the water level in your display tank will drop to the top of the lowest drain inside the overflow box. I would seal it even if it was a slow leak since if you had an extended power outage you risk having your sump overflow.

[Elo500]

Which kind of silicone should I use to fix it?

[ezerasurfr]

http://www.amazon.com/Aqueon-Silicone-Aquarium-Sealant-3-Ounce/dp/B0002ASD2U/ref=sr_1_3?ie=UTF8&qid=1462109676&sr=8-3&keywords=aqueon+silicone