What REAR diff. do I have in my '99?

[jo-e90]

Going to change the fluid in my '99 hoe after 200k. Manual says 80W-90 and no friction modifiers for Locking Diff.
I bought Mobil 1 75W-90 LS synthetic based on a search but dont know if I have standard axle or not. How do I tell? I have a GT4 in glove box but no G80.

 

[lesterl]

GT4 : AXLE REAR, 3.73 RATIO (DUP WITH 5 X 1)

From www.rpocodes.com

 

[jo-e90]

which viscosity??

 

[lesterl]

Man I dont really know for shure...... Sounds like you just got a straight axle, probably nothing special......