Mercedes introduced the TD (tourist/touring diesel) for model year 1978. With this '77 300 td, there must be a typo or something. Sometimes people will list their 300D turbo diesel as a "TD" for turbo diesel. Regardless, in the sedan 300D, MB didn't have the turbo enigne until modely year 1982. Possibly this car your going to look at is an '87 300D "turbo" (MB dropped the name "turbo diesel")

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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