No wiring harness problems for this model that I am aware of...

A/C repairs in general are very expensive.

At 140k in NY, your candidate would be about due for a full front suspension/steering makeover if it has not already had one.
This is a collection of small things that adds up quickly.
If I had not done the work myself, I would guess that I would have been out about $2K.

Motor should still have some life in it if it has been maintained.

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1986 300E 5-Speed 240k mi.