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.
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
President of CT/Westchester Section