1985 johnson 15 horse. replacing water pump, got the sierra 18-3327 kit. 2 questions. first, the small o ring in the kit, where does it go? I have matched up all parts with the existing pump installed except for the small o ring. Maybe the kit fits multiple models and maybe others use the small ring? Second, what is the purpose of the water restrictor under the seal in the water pump housing? It shows that it is only used in the 15 horse model, not the 9.9. If you look at the schematic for the gearcase it is number 40.