Motor oil sludge -arrrrrrgh

Last time I cahnaged the oil from my wife's 1999 ML320 it had sludge in the oil cap.
Oil and filter is changed every 3-4000miles and I have always used a fully synthetic oil either 5-30 or 10W30 since new.
Should I be reading the small print of the class action or do you think this is just an indication of too many short journeys in the cold up here in New England?
Has anyone seen the same?
The goo (or plaque - if I stretch my dental analogy) was a2-3mm thick off-white heavy foam on the underside of the oil cap. However I have never seen this before. But then on the other hand the car had probably never seen such a large number of short shopping trips in such cold weather.
I figure it is crankcase oil vapour that has condensed on this cool part. But am I wrong and I should worry or just see if it re-occurs?



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