Just some food for thought. When I got my first 4x4 duramax Silverado, I joined the forum and it made my first diesel experience great.
One of the things I read and did, was change out the fluids in the front and back differentials and replaced with synthetic fluid. From what the engineers said, was the first 500 miles, the temp in the diffs can reach 350 degrees while breaking in and fry the fluid.
Instructions for the transfer case, was to drain the case, and fill with Schaeffers synthetic engine oil to fill line, then remove the vent on top and add 1 more pint.
I did this and have 250,000 miles on my 07, and towed 3000 to 12000 lbs daily for 5 years, and to this day have never had an issue.
I have used the Schaeffers 9000 full synthetic in the engine since it was new, and installed the dual bypass filter system, made by Amsoil. On our cars, I used Schaeffers 6000, synthetic blend, and am looking to use it on my Disco, at my first oil change, coming up. I am contemplating doing doing the transfer case like I did on the truck. Any thoughts on this from the mechanics on this site?

 

My opinion, but changing to synthetic fluids is a good idea, They handle temp extremes better, flow better in the cold, more uniform molecule size (better lubrication) last longer, etc. Down side is expense, and they tend to find leaks more easily. You may have to replace some gaskets or seals, but it will shift and run better with synthetics.

 

I'm a synthetic fluid enthusiast.

I kind of doubt the diffs heat to 350 degrees, but if it has worked for you, keep it up!

 

Note, They said only in the first couple of hundred miles, while breaking in. I will say, my rear fluid was black when i changed it after only 625 miles, and checked it periodically after changing and was clean ever since.

 

I can imagine in a brand new item like a diff in the first few miles before the mating surfaces bed together properly the friction is far greater than usual use. Do the temps reach 350? Maybe.

I'm interested in using synthetic year round here in Ny. I'm sure the truck sounded different for the first couple of seconds starting in the cold here over the winter with Dino. I'm worried that is damage I can avoid. I can stomach the extra few $ on a gallon of oil. I've yet to see if I can stomach the extra leaks it finds.

 

If you off-road much, especially in wet, I wouldn't use synthetic in the drivetrain if cost is at all a concern. You should be changing the fluids more often.