I wonder if the crystallization/valve issues are less likely to occur for folks like me that drive the car a lot of highway miles (I put almost 500 highway miles per week on my car, typically driving 3-4 days per week) or if it is more related to ambient temperatures or just dumb luck.
I figure as long as the passive tank is completely empty when I service the car, I should never have DEF going through that valve that is older than 6 months. Along the same lines I wonder if I will ever really need to flush my system as long as I wait for the DEF warning before adding. I do keep a half gallon at the house in case I get the warning and can't get to a dealer for a couple of weeks.
10K and no SES - actually zero problems with the d whatsoever so far. I did an initial oil and filter change myself at about 5K, and the first official first dealer service is showing as needing to happen at 13K.
I can't imagine enjoying any other sedan more than I enjoy the d!