the goodwill replacement is not an official MB policy. from what i understand, the dealerships have an allotment of money every month that they can use towards this if they so choose. MB in Montvale, NJ told me that the official line is that any goodwill repairs are at the discretion of the dealer. the two major bugaboos of the M104 engine, namely the head gasket and wiring harness, are not part of any recall and there is absolutely no coverage for those components. i went through the same thing being a second owner. i have heard that in some states, they do provide this goodwill service even to second owners. in any case i would get a second opinion - it could be just the wiring harness which is about $500 + 3 hours labor.
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"