I know this subject has been covered a lot, but I still have a few questions that I could not find with the search. I have 32k miles on my car right now.
1. I'm thinking switching my transmission oil to redline superlite shockproof. Do I need to do a flush when I switch? If so, how? If not, is it alright to mix regular with synthetic? Also, that redline is rated at 70w90, but the manual says to use 75w90. Will this be alright?
2. I want to do my spark plugs too, but I do not want to use the platinum ones. I want to use the copper ones. I heard that they perform a little better, but doesn't last that long. I want to know the part number for the copper spark plugs for my 02wrx. Also what is the difference between the stock plugs and the "NGK 1 step colder copper plugs?" Which one is better?