Chevrolet Repair: oil in radiator

Question
Hi, I have an old 91 deville that i think i may have been driving daily for a  year or more with oil or tranny fluid in the radiator, first off is that even possible?  I thought the engine would go.  About 18 months ago i had the radiator flushed, and a few months later Jiffy lube wanted me to do it again saying the coolant looked dirty, i said no, i just had it done very recently.  I honestly until now never actually looked at the coolant which is a brownish color mixed with the coolant, so my thinking is wow- i drove it this long and its and old car, probably not worth the cost of a head or intake gasket job, but im amazed i drove it daily for 18 months probably like this.  I also suppose it is hard to determine if it is oil or tranny fluid mixing or is it?  Your thoughts?  many thanks   Marc

Answer
I have come across this a couple of times. Once it was a defective radiator where it was oil cooling line leaking in radiator tank..This is rare and usually the oil is not routed through radiator. Pressure is more than cooling system, so it's only coolant that is contaminated ,not the opposite. The other one was an intake cross contamination, which is most likely this car's problem. I have done many,many head gasket repairs and, funny ,Ive always heard of this kind of failure,almost as though it were almost as common as combustion gas leak, but I have not once seen this.