Do I have to put in a new plug each time I change the Primary oil? I watched a video and it said to use a new one. I'm coming up to my 9000km oil change and will go fully syn in all 3 holes.
Not necessary as long as you don't crank down on it. The older plugs (pre 96 engines) were a tapered pipe plug and cranking down on them would make them seat deeper each time eventually contacting the clutch basket.