Oh Boy…..Yes I do….additives… yep, all the time… what kinds? here you go…I have a 2006 Merc 200 Opti….I add all 3 merc Quicklean products when I add gasPlus Seafoam…Why?are you kidding?this boat needs to last me a looooong time, cuz. I would throw chicken bones in a corner if thats what someone suggested to keep the motor reaper from showing up.And… the opti runs great!!I fish year round in South La. so I want to believe I run the fuel out as I should…. but I still worry… Please dont crucify me on this, my brother does enough of that everytime I break out a bottle of something and pour it into the gas tank!!! HA!