Its a diesel 855 Japanese built motor.What machine/engine do you have? It's impossible to say 800ml of oil is correct without knowing what you are putting it in.
What issue are you having that makes you think the engine is nearing it's end? I personally have never worn out a diesel. All my problems have been outside the engine case for things like: filters, injectors, injection pump, glow plugs, water pump, alternator... Usually when I think it's an "engine" problem it has been fuel system related. When I have a diesel acting weak or bogging down when I think it shouldn't I first change the fuel filter(s).