W204 Owner Wants to Add a 12V Cooling Fan to the ECU

A 2009 Mercedes C300 (W204) owner recently replaced the engine control unit and is now planning a DIY cooling mod. During the job, an independent shop pointed out that this model has the ECU mounted on top, center of the engine, where it gets heat. The ECU already has heat-sink fins, and the owner noticed that by 2012 Mercedes moved the unit to the side of the engine, likely for better airflow.

The plan is to mount a thin, water-resistant 120mm or 140mm 12V PC-style fan above the ECU. So far, forum searches show no one has tried it.

Two questions remain: finding a switched 12V source at the under-hood fuse box that won't upset the car's electronics or trigger limp mode, and figuring out how much clearance exists between the ECU and the hood lining. The fan is roughly one inch thick, and it would need about half an inch to an inch of space above it.