I have a theory that the oil in the tubes also makes the intercooler less effective. I pull mine out every so often, and hot wash the inside of the intercooler with hot water and degreaser. ( like simple green or that purple stuff from coastal.) I lay it flat on the ground with the tubes sticking up and fill it with the hot water until it comes to the top of the other tube. Then sit and watch all the crud float to the top. If you ever wanted to know what makes it into your intake tract, you will find out this way. Dump it and blow it dry with a leaf blower. Probably totally un-needed maintnence, but it helps me sleep at night.
I need to set up a charge air temp guage and get before and after numbers just to see if it has any effect at all.