skimmer connection leak

Hi, I just found that the skimmer entrance has a small leak that is draining into and around the outside of the skimmer canister. I was able to use dye and found the source per the pic below. What kind of sealant can i use around the trim that can be applied on a wet surface? Or would i need...

I have a 40,000 gal in-ground pool, and, after much work and replacing of parts, we have determined there is a suction side leak at the connection at the base of the skimmer. Now that we've smashed up a bunch of concrete and dug a hole 3 feet deep, we're at a loss as to how to actually replace...