The steering box is leaking..... pretty bad actually. Some seal or gasket has definitely failed. Where are the seals/gaskets on these things? How many are there? How easily accessible are they? Is this something I can do or will I be forced to take it to the shop? Do I need any special tools – like air tools? Any schematics I can look at?

You might have to start learning German first, but there is an article related to this: http://www.mercedesclubs.de/scriptdaten/vdhforum/DCForumID1/4522.html

Otherwise try an online translator

Tom

If you need another gear box try
http://www.mavalgear.com/RemanProducts.html
Best to phone them at 800-338-9080 because their web site doesn't appear to list all they have available.

$460 (with core) for my 94 e320. Some on the list will caution about them being "adjusted" properly, although mine appears to work well out-of-the-box.

Bob

Its real easy to replace the input shaft seal and pinion shaft seals and the other exteranl seals once you remove the box. No special MB only tools required. Will need a pitman arm puller to remove that. And you will need to rechaeck the torque of the mounting bolts after driving is a few days after reinstallation.
Seal kits are cheap at the Dealer.

what is involved in removing the box? Just jack up the car (or maybe use ramps) and the rest should be obvious? any "tricks" to getting it out? Is this a 6am-to-6pm kinda job?

Just be aware it weighs the best part of 100#. Remove the fluid lines, the pitman arm, the steerig shaft coupler, loosen all the mounting bolts (4?), remove all but one, brace yourself, remove final one, lower box without dropping on pavement and breaking the casting.