10 out of 10 times in my experience it has been a blown headgasket. There would have to be a TON of condensation in the motor to affect the consistency of the oil to create a milky substance.

 

You just may have fixed your problem. A clogged PCV will allow moisture to stay in the crankcase and emulsify with the oil and then deposit on cooler surfaces such as the oil filler cap. It would be a good idea to let the engine get fully warmed up and change the oil and filter to get rid of all the slush. If the gunk does come back, then there may be some other problems.

 

Even my parents cars have some condensation inside the oil cap from time to time, until it shows up in performance or fluids start mixing and dissappearing I wouldnt worry about it. A good check up of everything never hurt though.