Lots of moisture ends up in the the crankcase, so it's easy to come up with water.
The earlier 4.7s (like my '03 durango) were famous for forming a brown oily foamy glop on the oil-fill cap.. the pcv valve was in the oil fill tube; the crankcase vapors would flow up the tube, the water vapor would condense, trap the oil vapors, and deposit on the coldest surface around (the oil cap). This mess would 'melt' on a long run (where the face of the oil cap would get very warm), and leave a brownish-reddish film. Which would then get the next layer deposited on it, lather, rinse, repeat.
That's just to say it isn't time to panic.
2014 WK2 Overland 5.9L
2007 WK Limited 5.7L
And some past Durangos
Red WK #19, Hemi #68.. I think..
Durango Owners Club DOTY 2011
"Must have been that yesterday was the day that I was born"