I can comment only on the oil change. They don't get a whole lot easier than on an '86 300E...with one exception. That fiber drip plate (it's not really a skid plate...it's too light) should be removed to make things easier. The space they left in it to access the oil pan drain isn't big enough to accommodate turning the tool once you have it on the plug. If you do manage in spite of it to get the plug out, the initial rush of hot oil passes over the access hole and manages to lay in a puddle on top of that drip plate. There are 6 screws (not all identical so remember where they came from) holding it on, and remember it's easier to take off than put on! Personally mine is out in the storage shed.

Good luck with the other questions.

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1996 SL320 97K miles
1996 C220 130k miles
1992 500SEL 170k miles <---sold
1986 300E 216k miles <---sold