I would imagine the best case for a seal would be to have equal pressure on both sides.
Since internal gas is compressible it would be easier for water to enter with a pressure differential. Then, because the water would have to be next to the seal with pressurized gas behind it to exit again, the water would probably stay.
Having a non-compressible liquid inside would make the seal work less in most cases.
I would imagine the best case for a seal would be to have equal pressure on both sides.
Since internal gas is compressible it would be easier for water to enter with a pressure differential. Then, because the water would have to be next to the seal with pressurized gas behind it to exit again, the water would probably stay.
Having a non-compressible liquid inside would make the seal work less in most cases.