I just cleaned mine and I used some all purpose cleaner/degreaser on the outside. I took it to a local carwash and sprayed it with the high pressure hose. Some of those bugs were still in there afterwards; so I used a piece of wire to carefully scrape them out. Yeah, I lost some paint too, but I had to paint my intercooler anyways. HTH
1987 GN 14" K&N, adj. wastegate, adj. FPR, XP Armstrong hotwired, 160*-stat, Hooker 2.5" catback exaust, Thrasher chips, shift kit, trans cooler, vdo boost/oil/temp guages, scanmaster II, Kirban's front/rear frame braces, GNX wanna-be rims, and the rest is stock..except for all the stuff that doesn't last 15yrs.
1987 Cavalier Z24 daily driver. 3-chamber flowmaster and 135db worth of stereo.
Remember everything is getting lodged in the IC from the front. So spray it from the back. If the paint is coming off the fins, don't worry about it. Technically speaking, that thick layer of 14yo paint is probably hendering heat transfer. I bet the bare aluminum would transfer heat better any way. Plus once mounted in the car with the scoop installed your not going to see it.
For cleaning the inside, brake cleaner works great. Buy 2 or 3 cans, wear gloves and goggles and just go to town on the thing. Spray an entire can inside the IC at once and slosh it around. Spray the fins, ect.. When there is no more black crap coming out of the IC, spray it out with water real good. Let it dry and reinstall it. Then make sure you will not end up with more oil in the IC by putting the plug on the turbo inlet bell and making sure the turbo is healthy. Shouldn't have to clean it again.
I use 2-3 cans (pourable, not spray) of O2 save carb cleaner such as Gumout. Duck tape the openings on the IC and slosh it around, then pour it out. Lay it in the sun for a while or hook up a shopvac to it and dry it out.