Given the pretty sudden no-start or start with ether and no idle affliction so soon after the incident with fuel types, I would not suspect something like valve adjustments right off the bat. Not that the valves shouldn't be checked, but I would be surprised if the combination of events needed to bring about the reported behavior depended on something that has such a gradual rate of degradation, and that it would affect nearly all the cylinders at the same time. But that doesn't mean don't check and adjust the valves. But, even if they are out of adjustment, don't be surprised if that doesn't fix things, unless the gaps are huge, meaning the all the valves open late and close early or tiny meaning they all open early and close late. Even one being significantly off doesn't explain this behavior.

Jim

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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)