I just replaced the vacuum diaphram on the distributor (same as yours for the W111) due to a slight leak. Dealer list was around $190....luckily I was able to obtain it for $127. Still! I think they are around $35 on a late model MB!

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All the best,

J. P. Mose
1968 250SL
1970 280SE 3.5 Cabrio
1987 560SL
1990 560SEL