What fluid in the differential of a 1989 78-passenger BlueBird All-American

[BlunderBus]

So, I sheared off an axle, and found a replacement, but it is sitting on a bit of an incline, with that axle downhill, so I've lost probably 3/4 of the fluid out of the diff. What fluid do I add, and should I drain it completely and put in all fresh?
I've looked around, and found a tag on the diff that's hard to read, but I can make out "Rockwell International", and the model looks like it might read R 125NX 7
Thanks

 

[Dragonpop]

check out this link, You probably need a GL-5 lube and the type of differential will determine the viscosity. http://www.wanderlodgeownersgroup.com/downloads/ROCKWELL FIELD MAINTENANCE MANUAL.pdf

 

[Booyah45828]

Gl-5 rated 75w140, we use Valvoline but whatever brand you feel loyal to will work. If it has limited slip or is a two speed you might have to include a friction additive in the fluid for it to work properly.