Well, I removed the seal in the middle of the night and thought I could remember the orientation of the seal for a few minutes but when I wanted to put on the new seal I wasn't too sure anymore.
Neither the parts catalogue nor the shop manual show/mention the correct orientation.
Should have made a photo or a note, I know.

Is the seal's correct orientation as in the picture? I.e. open side towards the gear box?

Thanks a lot for helping.