sublettm,

I encountered this exact problem a few years ago on my 240D and the diaphragm you have that has failed is in the mechanism that is shutting the fuel off at the injection pump, I believe. When this happens the vacuum line to the starter switch draws oil from the injection pump and into the switch mechanism. On my car it leaked a lot of black oil all over the panel above your legs, and then ran down the side of the center console, making a black stain in my palomino covering next to the driver's right leg. Nasty.

I do not recall the new part being particularly expensive, or cheap for that matter. I had the dealer do the job as I was unsure of how much of the vacuum system was shot. Turned out it was only the mechanism on the fuel injection pump. I do not think there are any other places where engine oil can get into the starter switch though.

Hope this helps, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)