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Old 04-14-2009, 01:50 AM   #1
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Default Motul or Amsoil Gear Oil for the 6mt and STi Diff?

I have read the gear oil faq's, unabomber's threads and just got done searching nasioc and iwsti. Trying to figure out what would be the better route to go.... Please don't post anything about the 5mt and wrx diff, this is for a 2004 STI...

Was thinking between Amsoil or Motul, also see more threads about Motul problems vs hardly any using Amsoil. This is what I was looking at.


Severe gear "rear diff"
Slip Lock "rear diff"
Long Life "tranny"


6MT Option A "Motul 75/90 and Motul 90PA"

Does the Motul 90PA require a additive?
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Old 04-14-2009, 10:30 AM   #2
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Join Date: Apr 2002
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You can ask Jesus, Mohammad, and the Dahli Llama and you won't get the right answer as there is no right answer. The Maintenance FAQ states the popular oils, use one of them. You are MAIC, so your best best bet is to use fastwrx.com as they are local and local advice is the best. Call Dan and axe him.
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Old 04-14-2009, 03:19 PM   #3
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The 90PA has the additive in it already. You can use the Motul Gear 300 in the front and the back without any worries.

-Dylan @ DS1
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Old 04-15-2009, 03:43 AM   #4
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Well I searched some more and still found more horror stories using Motul. Think I will use the Amsoil gear oil. Already using Amsoil 10w-30, larger EA013 Amsoil Synthetic Media Oil Filter. Might as well go all Amsoil in 3K miles which will put all fluid changes on 100K. Of course I might as well get a Amsoil filter and sock for the Aps intake, snag some Amsoil Synthetic ATF for the power steering and change the plugs.

How much of the 4oz bottle of Slip Lock is supposed to be added to the rear?
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Old 04-15-2009, 01:42 PM   #5
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Location: N.J.
04 FXT


Go with the Severe Gear in the front. No idea on the Slip Lock.

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Old 04-16-2009, 02:14 AM   #6
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07 WRX Limited 6MT
20G - SWP - SOLD


I've put Severe gear 75w90 or 75w110 in several Subaru rears. I've never used / needed the Slip Lock additive (in a Subaru).

Even in most vehicles that do specify the need for an additive, when using Severe Gear, the additive was not needed. I've only had to add it in one case, which was my brothers truck that tows a heavy trailer every day.
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Old 04-16-2009, 02:51 AM   #7
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1999 WRB GM6
2.12cc V9 Type RA


if your rear diff is plated, like spec c, I would highly recomend using PA90
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