I am not familiar with Mariner. On my Yamaha the impeller blades are pretty stiff and larger diameter than the pump housing; I don't think there is enough room for the blades to flip around as the shaft rotates. If that is not the case with your Mariner then sorry for the confusion. I lube the housing with a little grease on my finger and twist the impeller in the correct direction when I put it in. The shaft turns clockwise, you can look at the good motor running to confirm direction of rotation.
I did a quick search and found this. Good luck!
https://www.youtube.com/watch?v=OuilMAOMpgQ