Better to service the trans. than not service it. There is a step by step tutorial over at DieselGiant that you may want to check out. They also have a tutorial on the Power Steering.
http://www.dieselgiant.com/mercedestransmissionfluidchange.htm
The whole transmission service is pretty straight forward and very easy on the 300D.
I like to drain the torque converter. I like to get as much fluid as possible out of there. To find the torque converter bolt it helps to have a helper. One to bar the engine over at the power steering pump (22mm). And one underneath feeling for the drain bolt. It is a hex bolt. Same size as the trans. pan drain. I forget the size. You always want to turn the engine in one direction ONLY!! This would be Clockwise facing the front of the engine. NEVER go the other direction.
Use brake clean and compressed air to clean the pan. Nothing else. And DO NOT touch the bottom of the trans. with the pan off.
It took right at 7.5 qts. to fill mine with the torque converter drained. I have always used regular Dex/Merc III. Using synthetic should be fine.
You have the right diff. oil too.