1980 Johnson 85 water pump: Where does this O-ring belong?

[pkingco]

Hello,

I'm replacing my water pump on my 1980 85HP Johnson with a Mallory kit. Can anyone tell me where the middle O-ring (in the row of 3 small o-rings) in this picture belongs? I did not locate one like this when removing my old water pump. Thanks for any insight you can provide.

[boats.net]

One goes between stainless cup and water pump housing, one goes under impeller against wear plate and other one goes on drive shaft just below upper splines.