I use some food grade silicon and apply a thin coat the gaskets on my growler's and flip tops. Even stored at room temperature for a couple of months I can throw them on ice, serve them three hours later and carbonation and taste is just as or better than bottling.
I bought a tube around 5 years ago that I use for flip tops, kegs, growler's, and scuba diving parts to treat seals (NOT ON NITROX or TRI-MIX (enriched oxygen) unless you like big fires!)
I think I still have around 4/5ths of it still left. A little goes a long way to make a seal air and water tight.
In Primary: Belgium Chimay clones.
In Secondary: Braggot, pale ale, end of the world white.
Conditioning: Mead, Cider, braggot, Belgium Wheat.
On Tap: Clones, Chimay Blue, Red, Porter, malted cider.
Bottles: Far, far, too many to list.