On the W124 coupes check to make sure that the seatbelt presenters are functioning and that the backrests lock when you close the door. Also look and inspect the various door and window seals as they can cause air and water leaks if they are worn. Other than that those particulars, it is mechanically identical to a 300E from the same year. Any history or service records? The price is low so I would be suspect. There is no such thing as a cheap Mercedes-Benz.

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1989 300CE