I have a 02 firebird with the 3800 engine in it 49,000 miles, It looks like there is a small amount of engine oil in the coolant. The rad cap had a slimey brown buildup around the opening and fall. I drained the old dexcool out and put new peak antifreeze in but it still looks funny around the rad cap opening. I also thought i seen a very small amount of oil floating in the coolant. I drained the rad and really didn't find anything in the oil. Can old dexcool look like this and cause a oil looking build up at the cap???? Thanks