While not typically endorsed by the owner/operator of the car wash, I typically take mine to one of those places with a high pressure wand for cleaning your car and blast the crap out in a few minutes. I typically put enough money in the coin slot to wash down the wall and the floor when I am done.

I have found solvents and brushes to be minimally effective - it is mostly elbow grease that gets the job done by that method in my experience, and I share the experience that it gets all over your hands and the work area doing it the elbow grease way. I spent more on a gallon of that green solvent, Kerosene, Diesel fuel and a bunch of high powered solvents from various sources the first time I did this than doing the job 5 times would cost at the car wash. I even let is soak over night. Still acted like soft tar.

The car wash method leaves a mostly shiny aluminum surface. There are some places you can't get the proper velocity on and a thin smear of residue will remain. If you are bothered by that the surface can be approached by the elbow grease method - much easier and practical once the bulk of the goo is gone.

Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)