Here's a thought guys...
Oil vapors atomize in the cylinders, and blows through the intake system and coats our valves with gunk - we all know this and we've seen the pics of the valves
However, has anyone taken a look at the injectors to see if they are also covered with any amount of gunk?
I came from an Impreza STI before I got my 335, and if you don't already know, blow-by is an inherant issue with turbo cars but was extremely problematic with STi's (even with a catch can).
During one of my engine builds, I inspected my valves and yes they were coated with gunk just like our 335's, but I also noticed all four injectors were covered in gunk too. This caused a lean condition and random misfires.
Now, I don't know what these injectors look like or if these is possible with a DI engine but it is worth noting that atomized oil can solidify on the injectors over time.
Has anyone in here seen a set of injectors after 50k miles or so, or has anyone tried running some injector cleaner through (for injectors, I understand it does not touch the valves in a DI engine) to see if it helps the issue here?