It sounds like the #5 injector has a propensity to be the first injector to have failure. Others with the 2006 325/610 engines went through the same failure first, then some had other injectors fail after the #5 was replaced. Some opted to go to aftermarket injectors and not bother with the stock replacements.
Sounds like better filtration is needed, or at least this has been the census of opinion all along by those who have experienced failures. Many have installed better filtration in an attempt to avoid injector failures, of those, I wonder how many have still had injector failures or possibly avoided them? Maybe that should be your future consideration?
I installed the GDP 2-micron with the big line kit. The only white smoke I get happens when temps are below 40* and then it is only a slight puff right at startup. I have had occasional rough idle, it happens right at startup, gone in a few seconds. I also have been changing my stock cannister fuel filter at around 5-6K.
I used to run PS, now I run Opti-Lube XPD, I have had less instances of white smoke since changing to the XPD, in fact I had a lot more last winter on the PS and have had none this winter on the XPD. I also got the most recent ECM update a month or so ago and have had no rough idle since either.
CD