Now I'm confused about Rear Diff lubes What to use?

[cowboywildbill]

I was reading a previous post about breaking in the rear diff. I drained and replaced the fluid the other day on our 06 3500 at 2,000 miles and I had the goo & fuzz on the plug but no metal chips. I have towed several times after the 500 mile break in period. I replaced the lube with Mobil 1 75-90w synthetic.
I was under the impression that this was ok to use, but in the post it said to only use the GM lube and that the Mobil 1 could harm the rear. Did I misunderstand the post? Can somone shed any light on this? On our last truck I used castrol or or some off the shelf synthetic lube and didn't have any issues in 65,000 miles. Thanks

[DmaxMaverick]

Curious. Which thread are you referring to? I'm not aware of any problems with folks using M-1, or any major synthetic. Are you sure it was referring to the rear end you have? There has been much discussion regarding other rear ends, and locker/LS types.

[upsguy]

The manual says it should meet GL-5 spec. and Mobil 1 does. I put the same oil and weight in mine last weekend when I changed out the rear diff cover.

[cowboywildbill]

Thanks, I think I was reading an old post that was reposted. I might have misunderstood it. I thought it said that the only fluid that was lifetime was the GM stuff? I think I ran Valvoline 75-90 synthetic in our last truck and never had an issue in 65,000 miles. I have 2 quarts of the Lucas 75-90 synthetic lube I wonder how that stacks up to the other brands? I have friend that added 2 quarts of a different brand to his rear diff. They were all 75-90 synthetic, so far he hasn't had any issues.