I recently picked up a Foxwell NT510 Elite for my Honda and later added the Ford Module (and will probably add the Hyundai module). They also have a Mercedes module. In a quick google for reviews it seems to be decent for Benzes. YMMV

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1991 300D 2.5 "Rocinante"
2002 Golf TDI "Teen Spirit"
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1984 300D
1966 Mustang I6 3sp
1985 Mazda RX-7 GSLSE
1982 Toyota Supra
1977 Datsun 280z
1971 Datsun 240z