94 E320--makes a nice cappuccino
 

During a recent oil change, I noticed some brown frothy sludge in the coolant reservoir of my 94 E320--kinda looks like whats left in the bottom of a cup that contained a delicious cappuccino. My guess is that this is the result of coolant leaking into the oil system. In my limited experience, this is caused by a failing head gasket. What puzzles me is that I would expect to see this "cappuccino sludge" on the inside of the oil filler cap and top inside of the valve cover and not in the cooling system. Are my findings consistant with a failing head gasket? This car has 193,000 miles, leaks a litlle oil, and uses a cup or two of antifreeze about once a year.......Think I'll visit the Starbucks while I wait for the experts to respond...

The chocolate/cappucino brown sludge found in your cooling system is the usual sign of a failed head gasket.
Now, 2 cups/year is not really a terminal cappucino addiction and would not cause any immediate major problem.
I would suggest you closely monitor for any sign of increased percolation and take the necessary steps when coolant consumption increase to more alarming level.