I used to own a '80 300SD, which is the same 116 chassis as your car. I believe it's under the ashtray. I used to have the factory chassis manual for that car, but I sold it.

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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