Leaking Pentair light niche, suspect niche/liner gasket interface


New member
Sep 27, 2020
Toronto, Ontario
Hi all, I'm a n00b inground pool owner (came with the house) and I have a leak (~300 liters/day) somewhere. I highly suspect it's a light niche gasket. Vinyl liner, salt water, steel construction (I think).

Pentair/Amerlite large SS light niche w/ Intellibrite LEDs

Reasons: A) When opening the pool in the last 2 springs, the initial water level was just above the bottom of the lights.
B) I let the leak drain down recently and found that it didn't stop at the returns (or the skimmer).
C) slight signs of rust on my stainless-steel niche plate and liner
D) the initial spring level was a good 3" below the conduit port in the niche, which I feel I can rule out as the main leak

So my question is what would be a good course of action? I've ordered replacement gaskets (#79200400) though that's the one without the double wall gasket (unable to get 79200300). Would that be an issue?
I've also got 3M Marine 4500 sealant on hand. And I've heard that duct seal could work.
The liner is old, I'm thinking ~7-9 years old? Previous owner never turned over anything of that to me. Can I replace some/most/all of the gaskets if the water level is drained far enough? Should I? Or just I just try to seal as much exposed surface of the interface as I can? Should I wait till the spring to do that?

Thanks for any possible words of wisdom here. The pool was especially fantastic for this summer but I want to mitigate this before anything catastrophic happens.

Edit: My leak rate is worse

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