Based off your post the car in question is a W140 coupe. Starting off with fresh fluids and filters will be offer a good baseline to start of with, especially if you aren't sure about when they were last changed. Don't forget driveline fluids including the rear differential. Considering the low mileage there may not be to much to do. If the wiring harness is original then it is very possible that it needs updating depending on what year the car is.

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1989 300CE