Just got done rebuilding one (rather than just re-sealing) in a '93 W250. Getting a reman unit for around $200 is easier or you can get a seal kit for a lot less. Best to just remove the box to reseal or rebuild and to do the adjustments on it correctly.
If all you want to do is replace the pitman seal: Pull the pitman arm, remove the cover on top (leaving the adjuster alone) and pull the shaft out. Steering will need to be centered for the shaft to slide out. Snap ring is removed and drive the two seals and washers out. Reverse to reassemble.
A complete rebuild can get tricky which is why most just buy a reman unit.
