[Adam Skelding]

Sorry about the late reply, been pretty busy this week.
Replicating low diff oil is a hard job, if the oil is sticking to the gears it's doing 75% of the job. The remaining oil just flows round to make sure your diff teeth are always covered during rotation.
I try to keep on top of my diffs by checking them at the end of every meeting. That way if your car is running good, there's less chance of altering something you can't replicate.

Spool, like Mark said, put really thick oil in the front and thin the back out. Try not to go too thin on the back as you won't get much drive from the back of the car.
I've never had to go this far yet with the car, I've only ever run spools off road on super high grip carpet tracks to calm the steering down.