I have the 1.8D already and I know it doesn't have a seal. I am wondering of the G does because if so I might replace the D with a G so I can be better assured if I take my camera on holiday snowboarding that the water won't get in.
Yes, both the 1.8G and 1.4G lenses have a rubber seal on the mount.
You can see it on Ken Rockwell's review. It is the raised, thin black strip just outside the metal mount.