Oil filler cap
 

Opened my oil filler and there was a lot of creamy oil/water goo around the inside of the filler neck. I am NOT noticing any oil in the coolant NOR any other obvious signs of coolant in the oil (nothing on the dipstick). Just around the filler. So my mind travels to condensation or gasket leakage. Is this a viable scenario? I oiled up the gasket mating surface and it looks like there may be about 45 degrees of the gasket that may not be sealing. There wasere about 2 tablespoons of goo that I cleaned out. It has been about a month since I last had the cap off.

As an aside, I am only seeing gaskets for pre '93 vehicles. Do I need to buy a whole new cap for my '99 E320?

rjk, I would attribute the creamy goop to condensation. Commonly occurs due to frequent short trips where the engine fails to reach normal operating temperature.

Best way to tell is to drain a little oil after the car has cooled. Oil floats and this at the drain lug the water will come out first - usually white/milky. If not, then as said above.

The gasket for the cap can be ordered. I just put a new one on myself and it seals much better.

If it is just the condensation from cap or gasket, then just spend the $6 or $7 for an entire new cap.

What engine oil are you using?

Most modern expensive oils have additives that are meant to reduce this gunk.