Did it at 65k, didn't bother doing it again.
I also had no injector problems or turbo issues despite the scare stories and it actually was nicer to drive after the map (speed aside). However, as I said before if you've got a leggy version, ignore what BMW say about the diff oil for life nonsense. It really does need doing (mine had had quite a hard life to be fair) and is noticeably better afterwards. Big job though as (my understanding is that) they have to be taken off to change the oil.
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See, even made it to Spa...
If your going to accept having "ruined" handling that comes with the clumsy 4wd system, you might as well get an Audi, as that way you get a nice interior to look at.............
(you have no choice in F series, as 335d is Xdrive only now iirc!)