I echo the OP's message. I changed my rear diff fluid for my 2013 STI at 1,100 miles and it came out BLACK. YIKES

 

I have done mine every 20k and there have been no problems. Sure, the first time was a bit darker, but it hasn't had any effect on longevity.

Also, Subaru doesn't say to change every 30k. Only to inspect. I do it more often since I consider my driving severe use at times. Most people would do fine to let it go much longer.

 

I changed all of my fluids, at 30K just for the peace of mind, since I bought the car, used... Transmission fluid looked like it was new... probably got changed at the dealership, but rear diff came out black.

 

Here is what mine looked like after 17k:







NOTE: Blackstone's comments are next to worthless, so please disregard.

 

What is the best Oil for Rear Differential and Transmission ?
2013 STI

 

I use Red Line 75W 90ns all synthetic.
I'm not sure if it's the best one, but definitely it's one of the best

 

I changed both rear diff and front diff/tranny at around 3 or 4k miles. Used Amsoil severe gear.

 

Any thoughts about Motul 300?

 

I did this in my 2013 WRX when I first got it, with Subaru Extra-S in both the front and rear. Now on my 2014 STi, I would like to do the same, but I know you have to use a different type of fluid for the rear differential, I think? Could anyone chime in on the proper fluids to use for both the front and rear. I was thinking about going Subaru Extra-S for the front again.

Or would you not recommend changing the front, but rather just the rear?

 

Changing the factory fill that quick is overkill and definately NOT needed,if it the gears and clearances are set up properly(wich they will be). Differrential fluid will come out dark after one week if you change it that fast from new anyway. I changed my factory fill at 60,000 miles, looked fine, and did it just for maintanence.

Engine oil would make more sense to change that quickly, but not diff or trans fluids.

 

:eek2:

What does gear clearance have to do with gears/lsd breaking in?

And no, diff fluid should NOT turn "dark" after 1 week

 

Looks like Subaru's Extra S Gear Oil,or Motul 300 is the way to go.
Want to keep my STI for a while, and judging by all the comments on the Forums,and my personal experiences with the differential oil,it would be wise just to change it.
Thanks for chiming in