I checked my dipstick and saw I was running a little low so I popped my oil cap to add some oil. When I opened it and took the cap off underneath the cap I saw a crusty yellow bubbly substance all underneath the cap. I seafoamed my car about 5k miles ago, is this a product of the seafoam? Is this a telltale sign of a gasket leak somewhere on my motor? What is this stuff? I'll take a pic of it and upload it in about an hour.

 

The milky brown is a water/oil emulsion that forms on cold portions of the engine. In the winter months, and particularly when the car is only driven for short trips, its is normal. The blowby gasses in the crankcase contain water from the combustion process, and some of it will condense on the cold parts of the engine, forming that sludge. If you only take short trips in the winter, take longer trips and drive it harder. If the car sits unused in the winter, starting it periodically, but not getting the oil up to full temperature will make it worse.

Only thing you should check is the PCV valve, to insure its working, and pulling the crankcase vapor out of the engine.

 

It is not unusual to see a little something on the cap in the winter time. Especially if you short trip your car a lot. That is a common place for moisture to collect. Clean it up and keep an eye on it and for any other problems.

 

What's involved in checking the PCV valve? What's a good way to test it?

 

yes, i put maybe 100 miles on my winter stored z28 in 5 months and theres condonsation all on the oil cap.
its fine.