I daily drove a '80 SD for many years, the climate system is by far the weak point. Eventually the window regulators went out as well. w116 regulators were absurdly expensive when I looked for them.

I bought a '82 300D for less than new window regulators would have cost, sold the SD and have driven the '82 about 20k since then.

I personally think the W123 is easier to source parts for, while having the cooler styling like the W116

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1982 300D (w123, "Grey Car")
1982 300D (w123, "Blue Car")
2001 Ford F150 "Clifford" (The Big Red Truck)
1997 Dodge Ram 2500 12V Cummins
1996 Dodge Ram 2500 12V Cummins
Previous Vehicles:
1995 E300D, 1980 300SD, 1992 Buick Century, 2005 Saturn Ion