My car is a 500E...

My understanding of how the SLS fails is as follows:-

Bouncy Ride is caused by porus diaphragm in the spheres, creamy hydraulic oil at sphere.

Eventually the sphere fills with hydrulic oil giving a solid bone shaking ride.

The damping comes from the hydraulic oil entering and leaving the pressurised sphere.

My hydraulic struts were not leaking but were knocking. Replacing them reduced some of the knocking. Changing the top strut rubbers helped reduce knocking. Changing some suspension struts reduced knocking.
New spheres restored the damping. I did not touch the levelling valve at all. Now the SLS is restored to good working order.