Brown contaminant in coolant


2001 3.8L v6 Mustang (162k miles)

I had recently had my heater core replaced, and i am now seeing contaminants in my coolant reservoir. It looks similar to engine oil, and am hoping that is is not a blown gasket of any kind of crack. My oil does not look foamy through the cap or dipstick. I have attached a photo of the inside of my coolant reservoir, seems as though it is just floating above the coolant which seems like it may be oil?

Edward S

Last year had the same thing, except i knew right away it was a headgasket. Not saying yours is, but they are very suspect on these cars it seems