I had a similar symptom in the 300SD. I found that the nut holding the lnkage to the servo was very loose. Once I tightened it the problem went away. I think the servo was hunting to compensate for the linkage being loose

Worth a shot anyway...

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Current
Monika '74 450 SL
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FoxyCleopatra '99 Chevy Suburban
Scarlett 2014 Jeep Cherokee
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'74 Jeep CJ5
'97 Jeep ZJ Laredo
Rudolf ‘86 300SDL
Bruno '81 300SD
Fritzi '84 BMW
'92 Subaru
'96 Impala SS
'71 Buick GS conv
'67 GTO conv
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