This may help a fellow hatch spec C owner avoid the mistake that I made, although they will probably be a bit more switched on than me. Just done my 2nd gearbox and diff oil change at 53000 miles, having done the 1st one at 25000 miles. The hatch spec C has a mechanical rear diff, and although I have a jap manual, it wasn't clear what oil to use , so 75-90 LS oil was used front and rear, and it was quite noisy. This time, with the aid of google translate, it was clear the diff oil should be Subaru LSD oil, which was originally a 90 ls oil. So I used one litre of Titan race gear LS 90 in the rear diff, and 4.1 litres Millers crx 75w90nt+ in the front. If you have the STI flexible lower chassis brace at the front, it will obstruct the front diff sump plug, so one side of the bar needs to be taken off. There was hardly any metal on the sump magnets, so little harm seems to have occurred over 28000 miles, and the drive train all sounds much quieter.