What you describe sounds about like mine. The rear susp is very stiff and there is no adjustment ever required to my knowledge. Most people screw the system up when they attempt to tune it. The hydro-pneumatic compensator (bellows thingy attached to the rear diff and frame by linkage) is set by the factory to achieve the proper ride height. The dampening characterstics are set by the valving of the struts and the hydraulics.
I've been told by several techs that you only replace struts when you see leakage, pressure spheres are good for 100 - 150 k miles (mine are good at 215 l but the car is pampered), and the h-p compensator as needed for leakage also.