Hi,
This is a known issue with the 335d so don't worry too much.
The fix is to replace the red flexi hose and also a breather hose that can become dis-lodged and blocked over time.
The hoses have a poor interferrence fit and that is why over a period of time they start to fail, this allows a very small boost leak and will result in a fine film of oil residue building up, this is most visible on the red flexi hose and also on the drip tray.
When you next pop into your Dealer tell them that there are "PUMA" cases that are still open reference this issue and that other 335d owners have been affected, but have had this issue recitified. After reading the PUMA cases they will realise that there are a recent new type of hoses that can be fitted, and these should then be fitted to your car.
As this has never been flagged as a recall then there will be many 335d owners driving about totally unaware that they have this problem, so if you have a 335d then please check - the place to look is as follows;
1. Open your bonnet
2. Stand just to the drivers side of centre
3. Look straight down in front of you, looking between the front of the engine block (just to the side of the airbox) and the back of the Rad / IC
4. You should be able to see a red flexi hose....check if you can see oil collecting on it, or check just underneath and see if you can see oil resildue on the undertray.....it should be bone dry (unless it's been pouring down, or you've just washed the car and a bit of water is still there)
Another thing to check is a breather hose which sits just under the corner (driver side to the front) of the engine cover, there is just enough room for you to check whether it's become dislodged or squeeze it to feel if it is blocked.
Read this thread -
http://www.e90post.com/forums/showthread.php?t=245214
Hope this helps
Jules.