Yours is an 83 300D turbo. All 1983 300D's were turbos.
Replace the line. DO NOT try and repair it. The size of the nipple lines is critical so it is best to replace the broken unit.
When working in the engine compartment injector side it is best to remove this line. It tends to get broken easily and it's very easy to remove while working on the engine.

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It is your "brake booster vacuum line". It's under "brakes".

Dave

__________________
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