Personally I'm not convinced (yet). The swirl flap installation is pretty much common to all BMW diesel engines I believe, so not just a 335d issue.
I was quite worried about this on my E46 330d (which was an auto - some early manual cars didn't have them) - but have not seen any real evidence of any problems on the E9x. That is not to say there is not a problem, just that I haven't seen one.
Maybe time for a trawl on bmwland for high mileage E6x/E9x stories.