Found this thread here for the front main seal replacement on a 603
603 front main seal...
Embedded in this thread is a link to the online MB service manuals for the 126 and 603.
If that link is dead this one is still good. It's for the 124 but it has the 603 engine manuals in there.
http://www.w124-zone.com/downloads/MB%20CD/W124/Main.html
Beware on the water pumps, don't get a Chinese one or you will be doing it again in a few months.
The steering on these is the old school recirculating ball system with a steering gear box. It is not like the newer models (starting with the W210) that went to a steering rack like on all modern cars. There are threads on here about rebuilding the steering gear box. A fluid change is definitely indicated. Easiest way to do this is pull the return (low pressure) hose off the reservoir, stick it in a container, and feed fluid into the pump reservoir. *DO NOT* let the pump cavitate (run dry) or it will be damaged. Have a helper turn the wheel back and forth with with their other hand on the key to kill the engine if you can't get the fluid in fast enough.
Tip for this forum (since we appear to be stuck in 2003 or so with this software, are del.icio.us and StumbleUpon even a thing anymore??), click the Search up in the title bar and then in the window that appears use the Advanced Search, it is much better.