a cracked head gasket between 2 cylinders would not make your engine leak. Have you checked your coolant yet? See how that looks.

 

So far the coolant looks clean and happy.

 

Mine was doing the same and I was sweating bullets over it. Talked with a couple of my friends that are dealership mechanics. They said that almost all late models do this worst in the winter. The only place you will find it is in the bottom of the cap because it is the highest point inside the motor for the moister to go.
If it is a crack you will most likely find this goop on you dip stick. But this is not 100 percent true. I took a marker and put a line on my radiator overflow just to make sure.

 

I've never seen that in any of my vehicles...

My girlfriend owns the notorious coolant leaking 3.4L V6 from GM - she gets some milk-shake residue on her oil-fill cap, and she needs the coolant topped off ever few months.

Has your level gone down any?

 

Its just condensation. Common occurance in the winter.

 

if you really want to check to see if there are any internal leaks, do a leakdown test on your cooling system. don't bother trying to clean the slime, it's only on the cap and part of the dipstick.

 

ok so the problem that your describing TG02Z71 seems to be happening to me. basicly i was driving home today (-45F Out side) and noticed that i was smoking a lil bit, my sts pvc sys was leaking a lil bit. so i go to check the oil and notice theres white milky substance almost like a grease from my oil cap all the way down the filler tube. so i think the worst and think blown head gasket or W/e so i check the dipstick and the oil was just fine so i hold the oil cap over the filler neck and start the truck and that looks just fine as well. i really dont know what to think. unless its just condensation.

is that the conclusion you came to?