the reason for adding 100kg (220 lbs.) of ballast to the rear of the car before attempting to adjust the SLS is because the system has pressure on the supply side of the valve. ie. the pump is before the valve. As a result, the system will force fluid into the struts, but not out of the struts.

I suspect the speed at which the struts return to their neutral state varies somewhat from car to car. On my 16v, it's noticable while my mechanic's 16v, has to sit for some time (or be driven over speed bumps so that the suspension compresses.

Try adding the ballast and seeing how things go.

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'94 W124.036 249/040 leder; 8.25x17 EvoIIs
'93 W124.036 199/040 leder; 8.25x17 EvoIIs, up in flames...LITERALLY!
'93 W124.036 481/040 leder; euro delivery; 8.25x17 EvoIIs
'88 R107.048 441/409 leder; Euro lights
'87 W201.034 199/040 leder; Euro lights; EvoII brakes; 8x16 EvoIs - soon: 500E rear brakes
'70 R113.044 050/526; factory alloys; Euro lights