Crank case pulls charge in, and then blows it up the transfers, so pressures should be alternating in the cases. The seal will always seal better in one direction than the other - the logic is probably that by having it backwards as in the pic above, the better seal will occur in the direction it is facing, that being it may blow some oil/compression out past the seal, but be less likely to pull air/dirt past the seal into the engine.
Given it's already fitted I wouldn't bother changing it.
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