I did a lot of research on how to look after turbo cars before I got the 335 and one of the things that were always advised was to leave the engine running at least 30 secs after a drive to let turbos cool a little since switching the engine off will cut the oil from them, so since I got the car I religiously leave it running 1-2 mins after a drive. My colleague at work has a 320d with start/stop, and it got me thinkig would that not make the life of the turbo a lot shorter with the oil being cut from it constantly in start/stop traffic probably while it's spinning too?