1) Tamiya shock orings as they don't leak.
2) Alloy shock preload nuts as they have an oring to keep em tight.
3) Smaller spur as it moves the motor back further for better traction.
4) Alloy or carbon steering rack.
5) Alloy drive hexes.
6) A decent circlip tool otherwise the diff won't last 5mins.
Nothing else needed. Diff balls aren't too necessary but easier to put in at the time of build.
