It happened to me, same symptom on a 600SEL W140 and many times on 560SEL W126. They are almost all the same system. What I did is that I readjusted the rear hydraulic valve and it worked fine. Sometimes you need to adjusted many times so you make sure that there is no air in the oil stream.

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Master Computer Engineer, A+, Network+, MCP/MCSA/MCSE 4/2k/2k3 - Messaging, MCTS, MCITP, MCT, Brainbench, ICDL and starting Ph.D

380SE 1984 <------- Totaled by flipping accident
300SE 1988 <------- Sold
Volvo S70 2000 <---- 4 family
Opel Omega 2002 <-- 4 family
560SEC 1989 <------ Sold
560SEL 1990 <------ Sold
560SEL 1991 <------ 4 my mother
560SEL 1989 <------ Sold
600SEL 1992 <------ Current

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