Expansion Tank Coolant leak (fixed), What to use to clean the spots?

[Bianca98]

A note on the Simply Green: BMW does not use the same quality paint process on the engine bay as they do on the exterior of the car. In my case, an off the shelf bottle of Simply Green was able to strip the paint off parts of my engine bay! Be careful!

Personally, I would make sure the components were moderately warm to help loosen grime and then use a good degreaser. I have had good luck with the orange/citrus based products. I recently bought a steam cleaner though for these kinds of projects.