How do you replace seal on 2003 freightliner steering gearbox?

Hope you like making a mess, because this process will.

Get a paint marker, and put matching marks on the steering column U joint and steering gear box, so you can align them correctly when you replace the steering column. Separate the steering column from the gearbox. There's a metal ring which holds the seal in place... remove it... make sure the PS reservoir is full (it's okay to overfill it in this instance, because there'll be substantial fluid loss).

Turn on the engine... chances are, the seal won't fully pop out, so there'll be some prying to be done. Once you see your PS fluid spraying everywhere, shut the engine off.

Pry out the seal, put in the new one... you'll need either a driver or... I believe it's a 1-1/8" socket I use as a driver when I hammer one back in (but don't quote me on the size, as instances of me having to make this repair have been few and far between). Get it flush. Replace the metal ring (it's usually just a flat ring, although I have seen them with snap rings before). Replace the steering column, top the PS fluid off, and wash the side of the engine, frame rail, and anywhere else which got sprayed with PS fluid.