94 cabriolet sludge question

[AV8oR]

I am helping to maintain a friends 94 cabrio V6.
I changed the oil yesterday and found a creamy tan sludge on
the bottom of the oil filler cap. A look at the drained oil  - BLACK
no bubbles! Is this an antifreeze pin hole leak?
The coolant level has been constant for the last 2 months!

I was just wondering - she got really scared that she needed
a new engine.

Thanks fellas!

Zaf

87 1/2 Coupe GT - "The Kidney Stone Remover"
(Koni, B&G Springs, Motegi 16", Sparco Speed w/ Sparco Harness)

97 Geo Metro - " PTU- Personal Transportation Unit" w/ whopping 55 hp!