Depends on the car,use, and the diffs in your impreza.
Castrol Syntrax 75/90 for GT/WRX
Castrol SAF X or SAF XJ 75/140 for DCCD/LSD cars
Redline Heavy Shockproof and Lightweight Shockproof is ONLY good on dog gearboxes, and your syncromesh standard impreza box dont like it at ALL. Stick to "ordinary" Redline Syntetic, and not to shockproof series.
For impreza dog gearboxes: Shockproof light/heavy is a good choice.
5litres is more than enough: 4L on the gearbox and 1L for the rear diff. If your impreza has a gearbox oil cooler(spec c), you will need more oil.
Last edited by silverwrxnor; 28 December 2007 at 07:25 PM.