I pulled the Lower unit on my 1974 Johnson 85 Hp , to replace the water Impeller , when I Got it Off right on top of the Impeller Housing on the Drive shaft was a small O Ring that was above the Housing it was kind of worn , & I want to replace it , But my ? is where does this lil O Ring Ride , the Housing already Has an Inside & outside seal for the drive shaft to ride thru & seal it , doe's this O Ring Ride on Top of the housing Above the seal or doe's this O Ring ride some where else on the Shaft , the only other Place that seems Logical for it to be is Up on the top of the shaft where the splines fit in the Power Head, there is a Machined Groove just below the splines, did this O Ring slip down over Time , or doe's it ride somewhere lower by Impeller housing where I Found it, I Have an exploded view of my Motor on the web , but it doesn't show the exact location of this O ring, Thanks For any and all Advice , Bill D.