Peter,
The nice thing about the W114/115 is that it rides so well. Also, the glow plugs and controller can be upgraded with an inexpensive kit made by Bosch. I installed it without much trouble and have never had a hard start since.

However, if any diesel you are looking at has been sitting, rather than being driven, I would walk away. I have spent over $4k on repairs related to improper storage. e.g. rubber rot, fuel tarnish, stuck rings...

You might look into a W123 diesel--bullet proof.
Edit: rust is everywhere on my W115, especially rockers and floor. K&K manufacturing sells replacements at good prices, put $$$ to install.

Cheers, Andrew Seidel.

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86 560SEC
85 500SEC Lorinser
83 300D Turbo
75 240D