Need advice, not so slow leak in sump

[Masonjames]

I would imagine if you try to putty it, your not gonna sleep wondering if it's holding up and any fix would be very short lived I would guess. You should be able to just cut out the inner seal and re silicone it no problem. Might as well re due the entire inner seal while your at it though. But that's assuming your sump does not hold a huge volume of water. If it's leaking through the seams the structural seam holding the tank together has been compromised and so has the structural integrity of the tank. The inner seal does nothing to hold a tank together, it's sole purpose is to protect the structural seam. So I defiantly wouldn't try to patch any leaking tank that holds any significant amount of water volume as I have stated above. But for the typical volume of water we run in our sumps, or a small tank, you should be fine re sealing it, and be able to sleep at night without a worry. But maybe check with denny and see what he recommends.