My wifes 91 suburban has an aluminum intake. Factory stock injection. I had what I thought was oil at the bolts on the intake. I found that the oil was just a film. Antifreeze is what was leadking it had bad gaskets on both sides. I guess thats common with dissimerler metals? I changed the gaskets and it all went away. Take a paper towel and soak up the oil you will probably find it is coolant with just oil sitting on top.
Charlie