Still have not confirmed where the "oil" in reservoir is coming from. There appears to be a very thin film after a couple days. The color is light brown, possible reddish. I put a couple of drops of both the trans oil and th mobil 1 in the coolant to compare colors but this was inconclusive. Several hours after my wife drove the car, I opened the coolant reservoir and there was still residual pressure. My question - if there was a head gasket or trans oil cooler leak wouldn't the coolant pressure be released fairly quickly when the engine is turned off? I still have not seen any evidence of coolant in the transmission or the oil based on the dip stick check. Any problem with limited driving until I can solve problem? S.O.S.