So basicly, you just bought this car. You know another source of grime build up is from the road it'self. Other cars leak oil onto the road and when it rains tha stuff splashes up onto the underside of your car.
As I said, just clean it, brake cleaner or simple green will do the trick. When I got my SL, that was one of the first things I started doing was to clean the underside.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member