Synthetic vs regular gear oil and ......
 

80w90 or 85w140?
Synthetic or regular?
How about 85w140 regular?

I run 75w140 Full synthetic and change it every year.

works for me

Do you go wading? Changing synthetic every year sounds a little unnecessary. I run 85-140 regular and change it every 8-12 months. My t-case leaks so I wont run synthetic until I do a reseal.

yea I run dino style 85/140 and change every January.. Diffs, transfer and transmission. its just a thing... this last year was a huge mileage year for me and Matilda. I think i drove her 10k.... Also as a result of a few deep water crossings the gear oil was changes more than once.. its cheaper and easy to change. I am however thinking of changing over to synthetic rotella for the engine during the winter.

For what it is worth, our Disco's came with systheric, granted not an 85/140, wasn't available then but is now and will prevent more wear the dino.

No wading to speak of; however, I work at a dealership so I get fluid practically at cost. I figure it's cheap insurance for the drivetrain.

Normal interval is 15k and that's for Dino

Hell yeah that's awesome.

How about valvoline durablend? It's a syn blend

In the DII owners manual and the RAVE repair manual there is no service interval for the power steering, ACE, differentials or the t-case.
Full synthetic gear oil will last 100,000 miles easily.