Same gear oil for rear diff and transmission?
 

From what I gathered from my repair manual and a recent sticky on this forum, it appears that different lubricants are required for the manual transaxle and the rear differential. However, ECS is advertising a 75w90 gear oil for the transmission and rear differential of my car. Is this a good idea? If so, could I use Mobil 1 SAE 75w90 gear oil for both of these parts instead?

I use it in em' both.
 

I use 75w90 in both, always have. Im using redline though in my trans, just cause its getting a little rough in second, but its also 30 degrees here right now. I saw a huge improvement when switching to redline from castrol. But i also put a jhm short shift kit and new clutch at the same time, so i dont know. Hope this helps man.

Thanks for your input. The temperature has been in the negatives here and I now notice a huge difference in the ease of shifting from when I lived down south.

I'm a big fan of Mobil 1, and like to keep things consistent, so I'm still wondering if it would be ok to put Mobil 1 75w90 in my rear diff. Don't really know how much different that would be than Redline or the other stuff that ECS sells.

M1 is fine.

I'm convinced. 6 quarts of Mobil 1 it is! Thanks guys.

GL-4 only in your gearbox, GL-4 or GL-5 in diffs. Sinchro has some copper or brass parts I heard and putting GL-5 in it will damage the sinchros. I put RedLine MT-90 in my gearbox and RoyalPurple 75W90 in my differential. Gearbox and transfer case share the same fluid.

See this
http://forums.tdiclub.com/showthread.php?t=151658

Redline MT-90 in my tranny and Redline 75w90 in the rear diff.

Like said above, it's more important for your tranny to have GL-4 and I don't know of many others besides Redline MT-90 that are only GL-4.

Wow, thanks for the insight. That came just in time. So it's ok to use the Mobil 1 LS 75w90 in the rear diff, but not in the transmission?

Redline MT-90 and 75W90NS for gearbox/differentials: Quantity needed?
 

After a couple of hours of educating: I can second the above.

NO GL-5 for front (eats the 'yellow' metals, too slippery for synchros), only GL-4.

How much do I need for front (MT-90, may go with MT-85 for cold MI winters and fading synchros), and rear (75W90NS)?

Is Summit the best place to get it?

I just changed both my trans and rear diff last weekend. I got all my redline oils from FCP. Two MT-90 and one MTL in the gearbox and two quarts of 75w-90 in the rear diff. I think it cost around 65 bucks and free shipping.