Coming up on 20k on my 6 Speed WRX and i'm thinking of doing the transaxle and rear diff oil at 20k or 30k which is what the manual recommends. Subaru calls for GL-5 75W-90 for the transaxle and GL-5 75W-90 or 90 (i'm assuming they mean straight 90 weight gear oil? Not sure I even seen that before) depending on temp. I've seen people use 75W-80 for the transaxle but i'm not sure if that's a good idea or not. Anyways, what brand of oil/weigh should I be looking into?