I am a bit slow today. It just dawned on me that you haven't described anything symptomatic of the self-levelling. You may not have a problem with the self-levelling. Get another family member and stand on the back of the car, and have a third watch the wheel well rim in relation to the wheel. Or sight something against the roofrack and see whether it moves. Hop off and do the same. If your car moves up and down, move on to suspension stuff.
My tech says the systems are pretty robust. The shocks leak when they go bad. If they ain't leaking, they are probably ok. And they are $$$$, so don't go there if you don't have to.
The accumulators lose gas pressure, and if I recall, the ride is harsh, little to no "spring action". Some say it feels like the back end bangs over bumps.
1. Look for leaks at the shocks.
2. With the car on the ground, test your valve. Something should happen when you move that lever, or you should hear something trying to happen. If you see or hear nothing, rebuild or replace the valve.
3. If you get movement, adjust and test with a couple family members on the back bumper or in the cargo area. The car should go up when you all hop in, and back down when you get out, since you have already heard the valve working.
4. Test drive.
5. If it is harsh driving, replace the accumulators, $75-95, depending on who you talk to when.
6. If your shocks are leaking, replace em.
But if you are only worried about tire wear and noise in corners, you may be looking at the wrong things.
1985 300TD 4-speed 212K
1992 400E 343K
2001 E320 72K