1) I have no idea about the oil cooler, I have always just run the engine a bit to heat it up then used the drainplug.
2) These cars have fuel pumps? I have always understood that the pump on the engine(IP) pulled the fuel?
3) 31mpg mixed driving is impossible to attain in a 240D, at least it is on mine-- Shlomo has religiously returned 23-25mpg, nothing more, nothing less. I would *not* question the cars getting astronomical fuel economy heh heh
4) The cruise not working is a fairly simple fix(if the fix works) wherever you just reheat the solder joints in the amplifier and pray that it repairs what is wrong.
5) Welcome! You'll find anything you need to know here-- except vacuum pump interchange information