I have a 2008 Pro 4x, and it's got 119k on the clock. Are there any special additives I need to be aware of for the differentials or t-case? No, I haven't done the cabin filter yet, but it's on the list. What spark plugs does most everyone use. I was looking at NGK Iridiums. I know there may be a lot of opinions on those, I am just looking to keep it running great. I also run marvel mystery oil in every other oil change.