We took ours in for the fourth time last Monday. 2010 with 3K on it. Had this issue since the first weekend we owned it when we went to BMW Welt.
They ordered a part from Munich as they don't stock US specific parts. German spec 335d's don't have Def. Should get it put on this Monday/Tuesday. They couldn't explain what the part was cause I don't spreken ze Deutsch so well. I'll post up after I get the invoice.