After many many years i come back to my old post.

I have found draining plug and filling plug. It is the same, and differential and gearbox are together. Total quantity of oil is about 10.5-11 litres

And mrfixit, you were correct that it was full of water.

My new question is how can I prevent water from getting inside the gearbox?
Forklift is kept outside.

Also I did a brake job. And i might damage one seal from axle. Is this easy to replace? Where is located?