mercedes 420 sel fuel distributor

[LarryWard]

Put this question on mercedeslist and got some helpful tidbits but maybe some TDRs have some input on the problem. Namely a miss that now seems to involve 5 cyl and barely runs on the 3. It is a '87 420 v8 with 183k and did sit around a bit before given to me. Ran pretty good in beginning. Put in new plugs and seemed to improve some and did get up and go. Later it passed calif smog and very next day started up with a miss and occasional driving it seemed to get worse. Experienced friend mechanic said the fuel distributor diaphargms(thin rubber) with disuse are known to crack and fail. We eleminated ignition as problem but all of the new plugs even the ones that were on cylinders that were carrying the load, all were totally heavily black sooted. Another set of new plugs did nothing to eleminate the missing. It is obviously overfueling.

Found a source for rebuilts in Florida w.shping nearly $400 which is cheap compared to new or other rebuilts. Wondering what range of years of this engine interchanges adapt if I were to find one at PicNPull, etc.