I use 1.2 litres Red Line MT-90-GL-4 in the Datsun 5 speed transmission (also the Spidget 4 speed), and Red Line 75W90 GL-5 gear oil in the Spridget differential. For the steering rack, it's Royal Purple 75W-140, and Castrol ATF for Armstrong shocks (per AH Spares). For the engine, I've been using Castrol Edge but may switch to Rotella 15-40 T4; we use Valvoline VR-1 in a turbocharged BMW 2.5 litre that is stuffed into a 1972 2002. All of these (plus others such as Mobil 1 15-50) have the magic minimum 1200 ppm or higher of zddp (zinc dialkyl dithiophosphate). Red Line seems to have a very positive reputation for gears; I don't remember why I picked Royal Purple for the steering rack. I think that trying to understand and determine the optimum oil types and change frequencies for older vehicles is akin to Sisyphus, eternally rolling his rock up that hill. Doug