I think best spec ATF you can get . Choose one for the latest spec car. Don't go over board on price especially if using as a flush. I bought 50 lt several years ago for Merc E200 and been using ever since.
Chrome pipe definately on 2001 but may of been a year or 2 earlier. Is it red mudguards,. inboard rear brake, 4 pot front caliper If so think clutch plates probably latest spec.
Tried a good quality 2 stroke gear box oil once -replaced it and chucked the rest away after 1 trial - it can have that big an effect