ultrasonic cleaner or hammer/chisel

I guess you have to see how bad it is. Most use a combo of strategies including soaking, oven cleaner, pressure washer, mechanical, etc.

It can be a nasty job, though the Benzes I've seen don't seem to be as bad as others.

http://lh5.ggpht.com/_oawxQr-se-U/RuPqoWlgl-I/AAAAAAAAAf0/X42a-ZWmLKg/Cimg1499.jpg