80 was not a turbo but it does show to have the turbo intake setup. 1981 was a turbo. It may have been a fall of 80 build that was a 81 model.
Check for rust everywhere. Check the rear trailing arms for rust. $1100 each aftermarket. The rust just inboard of the shock mount and near the shock mount.
rust on the fenders just behind the wheels. also on the lower rear corner of the doors.
Check under the battery for rust.
Chekc for blowby by running the engine and removing the oil filler cap to see theblowby, A cheap way to do it.
Door locks, ACC controls-- vacuum. Ac control could also be circuit board.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car