Urgent: Overflow leak.. Advise required.

[JDigital]

So I am in the process of filling the Display portion of my tank of which I have dual overflows.

My left overflow appears to be sealed tight so far.. My right one, appears to have a very slow leak.. there is about 6" of water in the display section, and about 2" in the overflow.

I am using a Herbie style overflow.. if my main drain height is equal to the height of lower lip on my return bulkheads, in the case of a power outage, once the water drains to the lowest lip on the return bulkheads (and the highest point on main drain)

Will the water level between the DT and overflow equalize at the same height or will the pressure in the DT push through the leak and Raise the water level in the overflow ABOVE that of the Display area?