get a haynes... or get under it, youll find the drain plug... empty it and then fill it again from the top, iirc the box should take 2.0 ltrs of box oil.
i service my sax car 8-10 k miles, in that id do plugs, engine oil and box oil and filters.
its a few quit, imo its worth doing it every time, rather than the 60k people say.
what is 5er on oil and another on filters? ...