You need a new gasket for the crystal. These are hard plastic gaskets that are compressed on installation, and once they are distorted once they will never have the same holding power. I've given you the gasket part number, and they are still available from Omega, so if you know someone who has access to parts they may be able to get one for you, or you can use the part number to find a gasket on the open market.
Not replacing it would put the watch at risk of further water damage.
Cheers, Al