I have an alignment issue appears to be related to one side rear springs sagging lower than the other side. So I am replacing the springs. Ill do the spring pads too but are there some other parts I should be doing since the tension will be off the rear suspension? Like bushings?

I know I am bumping my own thread.....Sorry.

From some more searching I have come up with:

Trailing arm bushings and Subframe Bushings. Do I need MB parts on these?

I found this:

W126 complete rear suspension rebuild DIY

which should be a huge help

What about that differential support bushing that locates the diff?

At a minimum I'd do the diff mount. You're gonna be removing it anyway to drop the springs. How old are your shocks? They'll be getting completely removed, so if they're old or worn out, now's the time to replace them.

The rest of the suspension is up to you. Unless you're really a glutton for punishment, it may be a good idea to get this job done first, then rebuild the rest of the suspension another day when it's more comfortable to work on the car. Speaking from personal experience, just the springs/pads/shocks will make a profound difference on how the car rides and drives. Dropping the springs back out to work on the suspension later on just isn't a big deal so I wouldn't be too terribly concerned about the "while I'm in there" aspect of things. Once you've done it, it'll probably take you 30-45 mins to get the springs dropped the next time.

I forgot to say that I allready did the shocks.

Springs don't usually wear out, so are you sure that just one side sags and not both? Usually rear sag is caused by a worn out differential mount, but in this case both sides will be lower although not necessarily identical. I would replace this first. If the sag is still there after, then do the springs and pads and consider the trailing arm bushings.

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The LWB 126 is known for sagging rear springs on cars without SLS. Many people, myself included, have been through the "usual suspects" with incremental improvements, only to have the springs replaced be the ultimate solution.

Im inclined to do all of it. Have a master tech helper and a lift. Which of these parts are ones I should spring for the MB parts?

Shocks are done, If I do the springs, pads, subframe bushings, control arm bushings and the diff mount is there anything else to do?