2 cyl looper water pump gasket question

[ct1762@gmail.com]

The factory service manuals (all of them for all years that i can see 40-60hp) DO NOT show a gasket for the impeller plate... only an O-ring and nothing above or below the plate. I've rebuilt dozens, and have left the gasket that comes with the pump kit out on a few of them. Why do they include a gasket if it's not shown anywhere? On a couple motors, the gasket was put on top of the plate under the cup, and i can't see why that was done either as it has an O-ring. Anyone?

 

[racerone]

They started showing the gasket in the 1991 parts book.

 

[ct1762@gmail.com]

Right, but I should've said 1972-1988 models before the lost-foam block came in. Any idea as to why they include the gasket and can you leave it out? i can't find anything in the service bulletins about it and i've got em' all (i think)...