The hydropneumatic struts replace the shock absorbers, but you would still have springs, just differently rated than the ones on the non hydraulic suspension. (at least on the 123 cars I've heard that the spring rate is different...)

I don't know what goes into replacing the seal on the output shaft from theh diff, maybe one of the others will comment on this.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...