Case 580SL Rear Axle Planetary Oil Leak - O Ring Replacement Question

I bought a Case 580SM recently to replace my 580SL. I am getting ready to sell the L and want to repair a leak in the one rear axle planetary. It has had a slow leak for the last year and I just topped up the planetary oil every month or so but want to fix it before I sell so the new owner doesnt have to deal with it.
I purchased a replacement O Ring but want to confirm the procedure to install - If I remove the wheel stud nuts and remove the wheel and tire is the planetary housing free to be pulled away from the end of the axle ? Do I need to remove the planetary housing completely or can I just pull it away from the axle a bit and pull the O ring over the housing flange ?
If I have to remove the planetary housing completely are there any special procedures to keep any of the internal parts from coming loose or out of place ?
Appreciate any input before I tackle this repair.

As far as I can figure, you have what I call the "extended hub" version of the rear axle.
These are not very common over here.

No there is nothing really to worry about. There are a couple of countersunk screws that retain the hub to the flange.
They can sometimes be tight to undo, use a pin punch that fits inside the allen head & give it a few good hits before you try to remove them.
Hopefully nobody has used loctite on them or you may need a little heat to get them to move.

The 3 planetary gears are retained to the hub.
There is a short sun gear shaft, which may come out with the hub, but it should just push back in.
I would fully remove the hub & give both sides a good clean using a spray gun with some kero or diesel, dry everything with compressed air & assemble with new oring.

Yes I guess you would call it extended hub - the planetary housing is outside of the wheel studs. I have attached a copy of the parts diagram for my style rear axle showing the O ring I purchased.

Thanks for the tips on how to disassemble the planetary - I was hoping it was that straightforward but wanted to confirm before I pulled it apart and had a pile of small parts fall out.

thanks again, Gary