If you're using a Quaife, they suggest "factory synthetic" or at least NOT a RedLine Shockproof. Quaife is very quick to point out that RedLine produces an excellent product but that it the Shockproof doesn't play well with the Quaife differential. I remember something about "too many solids" but I have a lousy memory and am not an engineer by any stretch of the imagination.
For my 020 box, I use Mobil 1 75w-90...