Quest to find best presoak for automatic

Two weeks ago there was a little rain and it got my black ML350 Benz dirty so I washed it about 2 days later using my WashWorld. For some reason the dirty spots on the front hood wouldn't come off. I thought something was wrong with the equipment or presoak so I drove to a competitor's WaterWizard to test it out. Guess what? It didn't work either. The same dirty spots in the front won't come off. I know if I use my finger and rub it, it'll come off. I'm surprised I didn't see this during the winter months.

My setup uses an ACID pass then an ALKI pass. I think the presoak that will work will also remove the eyebrows in the front and back. What have you guys used and swear by it?

I use extremely strong alkaline presoak- usually a regular touch free presoak that has been boosted by caustic additive. Several chem mfgs have produced products designed to be used as a booster. You can actually just use bulk sodium or potassium hydroxide for the boost. You have to know what you are doing though, and it's still not a perfect process.