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I am about to buy an 08 WRX with 40k miles on it, have a feeling the 30k maintenance was not done. So I am going to do a rear differential fluid flush along with the transmission. I read a couple other posts (not sure if all years are more alike then different) and people are saying to put 75w-90 in both the transmission along with the rear differential. What oil should I actually use? Should I just go with OEM? First Subaru vehicle, sorry guys! Thanks for any help
 

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Don't put the oem (crap 75w-90). Go with Motul or Extra S. I've had Extra S for about 20k miles and I can feel the smoothness already wearing down. When I replace it again at 60k I am going with motul. And yes it's 75w-90 in both the trans and rear diff.
 

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Discussion Starter #4 (Edited)
Thanks for the input guys. I have heard a lot about Redline Lightweight Shockproof oil, would this be good for both? (x-mission and diff.) What about just using Mobil 1 75w-90, is this a no no?
 

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I would just throw Extra-S in there - it's great stuff & a bit cheaper than some of the aftermarket oils. I think you'll need 4 qts to do both.
You can get it in quarts at Fred Beans Subaru online. You may want to stock up on Subaru OEM oil filters when you buy the gear oil.
 

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Mobil 1 has been shown to be junk, don't know about their gear oils. If you use Redline, make sure the stuff you're putting in the transmission has NS in the designation (75w-90NS).

And, yeah, don't use OEM oil filters. .long discussion showing they're junk as well and many were just recalled. Mazda RX-8 Tokyo Roki black filters fit, same bypass valve, same quality as the old Subaru blacks.
 

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Another one for Extra-S. Had Motul in for about 3k miles and dumped it in favor of the Extra-S. One of the best (albeit on the expensive side) things I've done for the trans. I imagine the rear diff like me better too when I did this.
 

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Another one for Extra-S. Had Motul in for about 3k miles and dumped it in favor of the Extra-S. One of the best (albeit on the expensive side) things I've done for the trans. I imagine the rear diff like me better too when I did this.
Not protecting motul or anything but how can you tell the extra s was better?
 

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Not protecting motul or anything but how can you tell the extra s was better?
The motul ended up being very notchy feeling, especially when cold. Extra s provided a lot smoother engagement. I've run extra s in my trans now during both of my last oil changes (car is at 75k now) and I've never had extra s break down.

It may also be different uses of the car. I haven't drag raced it in almost two years, never auto x and no track days. So if you're one that pushes the car more, the results very well could be different.
 

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my 30k sevice i went with extra-s. at the end of this month im doing my near 60k service. i have motul for the tranny/front diff and leftover extra-s for the rear. i got a good deal on motul at wbm.
 

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Exactly. Extra S broke down within 20k miles of regular DD driving. Going Motul next.
I went motylgear first and now running gear 300 a of two week ago. Can't tell any difference yet maybe when winter hits I will
 

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So Extra S or Motul is the way to go for tranny fluid and front dif? How is the front dif fluid accessed? Is it different for reg WRX and STI?
 

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Under the tmic
under the tmic on the passenger side its a long handle dipstick. get a section of clear hose to put on a funnel to make refilling alot easier. the front diff and tranny is all the same fluid fill tube. dont overfill it cause you will never get all the old oil out. its just too thick. you will only use about 3 qts for the front and almost 1 qt for the rear diff.
 
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