Rear Self leveling inactive

[David-S]

Hello,
I am in the process of restoring my 1981,W123,230TE estate (Chassis no-12328322005307). At the present I'm working on the back axle/suspension.
But first a little background, since I first acquired the car, the self-leveling facility has never worked, although the rear suspension has never drooped or been hard. As the restoration has progressed I have found that both oil pipes(feed& return) are holed (new ones are ready to be fitted)+ the valve lever had been disconnected, on removal of the suspension, the struts and pressure spheres contained oil. On examination of the valve to fully understand how it works( My Haynes manual tells next to nothing) there appears no way that oil pressure from the struts/spheres can return to the reservoir tank.My conclusion, is that the previous owner, rather than pay for an expensive repair altered the valve to retain pressure in the struts.Could anyone please supply me with a drawing of the valve and components, so I can check my assembly also a detailed explanation of its workings.
Thankyou