The hydraulic system from my 16v is completely disabled, after several problems with shocks and 'oxygen bowls' (With the side-effect that I can't find the right rear-springs now).
The pump is kind of an exentric rotating thing which is connected to one of the camshafts. From my car I removed the pump, took out the parts which are inside, and placed back the pump, so it is still in place but does not work.
There is a company which sells a special plug to cover the hole after removing the pump.
At this moment I have this setup for some 6 months without any problems.
If your car has run over 150k don't spend much $$$ on the hydraulic rear suspension. If one shock has gone, the other will soon. I was quoted $450 each!(Europe) Normal 'Sportline'-shocks will fit well.

Good luck,
Robert Z
1986 190E 2.3-16
Holland