4.7 L engine fumes

I posted an earlier note describing a situation where I can smell gasoline-like fumes in the cab of my 2002 Ram 1500/ 4.7 L when idling with the engine warmed up and the outside temperature is colder than -15C. I've had the truck into the dealer several times complaining about this, but they've never been able to replicate the problem (likely because they're looking for the problem in the shop where it's nice and warm). I've also noticed a small bit of black, oily/watery fluid that drips from the engine when this is happening, and it has the same odor as what I smell in the cab.

A friend suggested that there is leak somewhere in the PCV system, as the odor I described fits what you'd smell from blow-by fumes.

Any suggestions from anybody? Is this a common problem for this engine? Maybe a cracked PCV valve or even a cracked manifold or leaky gasket? Why the odor occurs only at temps colder than -15C is somewhat of a mystery.

Have you gone under the truck when its doing this to see where its leaking from?