Morooka mst 500 final drive fluid change & other parts

I recently just bought a morooka/komatsu mst-500. I am going to change all the fluids in it and am confused on what the fluid level should be in the final drives. I did get a service manual for it, but it doesn't give any information on the fluid level or even the type of fluid needed. I assume 80w90 would be an appropriate type? When I look at a slightly lower serial number one the plugs are all in a line like most other equipment were the fluid level would be about half way up. On mine...

Morooka mst 500 final drive fluid change & other parts

Morooka mst 500 final drive fluid change & other parts