What am I looking at when I look into the holes in the back of the plastic box which I took my blower motor out of and I see fins. Looks like maybe my AC evaporator? Or is it my heater core? Either way it is partially plugged up with black soot-like stuff. How do I clean this stuff out? If I spray this area with brake cleaner, will it drip inside my car? Does the bottom half of the plastic box which houses the blower and also obscures part of this clogged up fin thing need to be taken out in order for me to adequately clean the fins? If so, how?

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87 300D 162,000 miles: It's not just a car, it's an adventure!