replacing differential lock parts

I am starting this thread to outline the steps - which I'll update as the work progresses.
In general I believe that only one side of the axle needs to be removed.
here are the steps, please chime in if I miss or overlook or get something wrong. Front and rear may be similar:

1: lift the SEE till tire can be removed, remove tire
2: remove stabilizer
3: use bottle-jack to support axle and remove shock
4: lower axle till spring is 'relaxed' and can be removed - no need for a spring compression tool to hold it.
5: disconnect lines/hoses (air, break)
6: drain differential oil and open differential case to 'separate' the one side of the axle
7: remove spring (#9) and dog gear (10), I suppose the rest (11-15) would follow?

At this point I am not sure if I also need to remove the drive-shaft to remove the inner o-rings. And if so if it would be better to also open the other side of the axle (wheel side).
I have ordered some parts, but it could take another week for them to arrive anyways - so there is time to make myself smart about this task.

The air locker piston is on the short side of the axle.

1) Drain some of the oil from the differential, if you don't like messy.
2) Place jack as close as possible to the differential housing, on the long side of the axle.
3) jack up axle, remove tire from locker side of axle.
4) Set differential housing on a jackstand of sufficient capacity.
5) Slightly relax the weight of the vehicle on the spring. I accomplish this with a farm jack (high lift) on the bed corner. It doesn't take a lot of lift to relax the spring at this point - in fact, it's easy to go too far, and it feels just like it's under tension but in the wrong direction.
6) Unbolt spring from axle perch side. Note orientation of spring retention clip.

7) Unbolt shock from axle side. If it's extremely difficult, remove nut, and attempt to press out bolt with a second bolt/nut combo (like a tiny screw press)
If you have a rear anti-roll bar, you'll want to disconnect that linkage too.
9) Unscrew air line from locker nipple on housing, and hydraulic brake line from caliper or drum piston housing.
10) Clamp brake flex line at transmission for rear hydraulics.
11) Relax parking brake cable assembly, and disconnect from combiner bracket (don't do it at the hub)
12) Use a transmission jack, pallet with blocks, or an engine hoist and begin to support the short side axle half. DO NOT apply lifting force that pushes the diff housing up. It's resting nicely on the jackstand and keep it that way.
13) Remove all the bolts from the short side of the diff housing. Two bolts that enter around the pinion output shaft don't go all the way through. Leave the bolts on the long side of the diff housing in place. They will keep things together on the other side of the axle you're not servicing.
14) Gently slide the short side straight out. Splines will disengage from the ring gear.
15) Axle housing is now floating in space - use air pressure to punch out the piston. Note the wear ring and return spring position on the stack.
16) Replace the square seals on the housing and the piston (there are two)
17) If it's excessively rusty, you'll want to scotch brite the inside of the axle housing. If there's a lot of pitting, you might need a new housing to get the locker to work. I've only seen one housing that was that bad.
1 Clean any abrasive remains with solvent/brake cleaner from piston and housing.
19) Pre-lubricate the piston and seals with gear oil and re-insert. Remember the wear ring and spring location.
20) Clean and buff the sealing surfaces of the axle flange and the differential housing flange. Use permatex ultrablack in a thin layer smeared on both sides.
21) Mate housings together, and reinstall bolts in a mechanically even fashion.
22) Torque all bolts on diff housing.
23) Reinstall spring in reverse of removal.
24) Reinstall tire
25) Test locker engagement with air pressure reduced to 30 psi and use rubber tip of air gun to actuate locker piston. Wheel should lock and not turn, then release with a crisp thunk. There should be no blow-by or leakage from the interior of the housing when under pressure.
26) Reinstall tire and lower to ground
27) reinstall remaining connections: anti-roll bar, shock, brake hydraulic, parking brake cable, locker air line.
2 refill differential housing with gear oil.
29) Enjoy having lockers that don't deplete your air system and/or blow gear oil all over the place.
30) Optional: Do this whole thing again for the front axle, taking into account the steering gear and second brake circuit. (at least you don't have a parking brake cable up front)

Great outlines - thanks.
for step16 to clean the housing - I take it that's the inside of the axle - do I need to remove the shaft?
If so, do I need to open the other end of the short axle when installing the shaft again, or does it slip right in place when pushing it in?

The axle half shaft will be securely fastened to the portal bearings, so it'll just be centered in the housing. When reaching into the housing, you can work around the axle in place. It's quite a bit more work to break down the assembly and pull the hub off the housing (it's not impossible, just more parts fall out like shims and whatnot)

Jiggle the hub on the axle end back and forth to get it to engage the splines in the ring gear.

in addition to the items in aaronsp's list, there is also the thrust arm (#7@Figure 128 ) at the rear and same on the front axle as well as the torsion bar mounting and steering Tie-rod in the front.
On the steering there is an option to either disconnect the tie-rod at the joint, or remove the mounting (#16@Figure 135). I started removing the mounting, but after loosening the lower screw (#18 ) oil came out and I tighten it again.
Is removing the joint the better way, so I don't have to deal with the wheel mechanism?
The parts I ordered have not arrived yet anyways, so I am in a preparation stage.

Oh yeah, totally forgot about the thrust arm (the two of them form a triangle on the torque tube and axle housing) Sorry I redid that rundown from memory. Good callout. As usual, if you can get the repair manuals for the U900/U1100 it'll help a bit. The other thing that's really handy is the mercedes "mechanic's handbook" which lists all the torques and specifications for a lot of items.

If you remove the lower tie rod mount, those bolts go into the gear hub. It's not a big deal to just drain the oil from the hub and refill later.

Today both differentials got replaced.
But in the process one brake line went south at the T on the front axle.
Now I am looking for a 6mmx550mm line with both ends flared.
The local autocrats have only smaller threaded flares on them (since I had the T with me I could check)
Expedition Imports sells all the parts and a 25' long tube: https://expedition-imports.com/TUBE
Only need about 2.5' - anyone has some tubing left I could buy? I could make my own but also do not have the tool.
Or does anyone know where to get the right size brake line?
UPDATE:
I found a local hose place which fabricated the line using 1/4" tube. and posted the info here:
https://www.steelsoldiers.com/showthread.php?170914-Brake-line-replacement&p=2047247#post2047247

Belmetric out of NH...talk to Matt. He carries Metric fittings and MB metric hoses. He's fast and knowledgeable of Unimogs to boot. He can also get you SS.

Great website too.

The SEE axles have the drain plug on the locker cylinder don't they? Often the locker piston can be freed up in the cylinder by flushing well with light weight oil. Oil in under pressure through the air line to activate the lockers, then drain the flushings. Repeat. Avoid steps 1 through 413!!!! If you get really lucky.