Yes, it's a turbo, all the US W116 300SD models were turbo equipped in 1980.

It ought to be checked out to be sure it is safe before it is sold. Disclosure of all faults is a good idea, but it should be sold "as is"

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1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)