David C Klasse,
I will take a swipe at one or two of the questions.
First, my 1986 model suffered a failure of both of the rear strut attachments to the suspension arms. The bottom of the shock strut has a steel thread that engages an aluminum mounting block. On my car the steel threads stripped the aluminum threads right out of the cast aluminum block. I was pretty sure this was a poor engineering job, as the aluminum tapped threads have no where near the capacity that the steel thread did, and there is no replacement aluminum block available. You have to buy new shock strut assemblies. I think the repair cost me in the vicinity of $700.
Second, the front shocks can be prone to failure. My right side shock failed in the first five thousand miles. Even though it was a grey market car, I sent the old broken one back to the dealer I bought the car from and he sent me a new one. Better than nothing. I have replaced both front shocks again since then.
Not sure about the other items as I like the heavier steering of this car compared to my newer 1998 E300D TurboDiesel and the 1999 C230 Kompressor models we leased for three years.
I have had idle problems as well, but my car is a manual. Once it was the idle control valve/motor, and lately I believe it is the need to replace the injectors. They are 16 years old and have never been replaced. I checked them recently and they do not spray, they dribble.
I would advise checking the valve lash as soon as you can. I did this routinely at about 30,000 mile intervals with relatively small changes. The last time I did it was closer to 50,000 miles ago, and I am sure that contributed to the burned exhaust valve I just took the head off to replace. I did not do the work, I took it to a very capable technician in the area, recommended by another on this site frequently. I just got the car back, or, in reality, my 16 year old son just got the car back. He "inherited" it from me last December. It runs like new again now.
Overall the car is much tougher than I thought it would be and I look for my son to see another 150,000 miles in it. Good luck, Jim
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
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)