I lived in Denver and now in Austin and I've never seen any indication of this. I really believe it's more a function of how long the car is driven at operating temps. My ususal drive is 40 minutes at highway speeds.

 

of course. As noted, with the tube and cap being so far from the engine, it takes a while to heat that up. a 40 minute highway drive is plenty to get rid of that.

i drive my daily MB about 2 miles a day to and from the train station. its got plenty of gunk in the cap.

 

Totally normal.