Gearbox / Centre Differential gear oil

Subaru Extra-S 75W-90 is a highly refined mineral gear oil. The gear oil is manufactured by a subsidiary of Shell in Japan and only sold in 25L drums. Extra-S is not only made to Subaru specs but is the factory full in the gearbox / centre diff and rear diff for the WRX. Whille Extra-S is not sold in Australia, I import it by the litre from U.S.A. The gearbox of the WRX is really fussy so don’t use a fully synthetic gear oil or you will differently get grind. Since this oil isn’t synthetic I would change it more frequently. Extra-S doesn’t like the cold so don’t use it is you live where is snows. I change this gear oil every 25,000 KM.

Rear Differential gear oil

Motul Gear 300 75W-90 is a fully synthetic ester (grade 5) gear oil. This oil works very well in the cold and hot temps. Gear 300 handles the heat really well which is important since the rear diff is small, only taking 0.8L or 1L for Australian models. Gear 300 lowers the noise of the rear diff compared to OEM Extra-S. Since this gear oil is designed for rally / track use I would change it more frequently. I change this gear oil every 25,000 KM.