I know you said that you have tried various SLS valves with no difference but... The SLS level valve has a pressure holding feature which ensures that the hydraulic struts, etc. have the proper pressure. I replaced my SLS valve in my 300TE after replacing the accumulators because the strut damping was inadequate. No issue with ride height however. The pump only feeds the high side (not the return line) and is self-limiting so I wouldn't think that could cause a restriction in the return line. Have you tried driving the car with the rod disconnected? Mark