More than likely, it wasn't the gasket that was leaking.
On a side note, you shouldn't need to put any sealant on that gasket. Cork gaskets are meant to be installed dry. My experience: they only leak it if isn't installed dry. Sometimes even with sealant (silicone) they will leak. Reason: it makes the gasket slick and it "slides" out when compressed instead of smashing like it's supposed to.
I hope you didn't plug the hydro drain hole with silicone......
