I am having some issues rebuilding my 40 horse mercury four cylinder. It's the square black pump. I have taken it apart and ound my new kit does not come with the rubber 'valves'? But instead has plastic washer sort of discs, are they supposed to replace these? I bought mercury kit number 21-857005A 1 from the dealer and he says it's the right stuff. Just does not seem right. I am an automotive mechanic by profession so I know something does not seem right to replace the rubber with this plastic washer disc?? Anyone run into this and could point me in the right direction? I was rebuilding the carbs due to a sticking needle and thought this was a good preventive maint. to do as well. Sometimes if it aint broke, leave it well enough alone....Thanks ahead of time for your help.