I'm going to change the automatic gearbox oil in my C180. It's a 1999 model with 5 speed gearbox. I don't think it has a drain plug in the torque convertor, so I'm planning on changing the oil by running the engine & draining 1ltr of fluid at a time through the oil cooler lines. But which one is the output from the gearbox? I'll disconnect it at the radiator end. Many thanks!