Well, since no one has jumped on this one, I'll take a stab.

Rust is a killer. That is probably your most pressing consideration. Make sure to look under those interior mats for rust and check the side rails and battery tray.

After rust, look for SLS issues, engine, trans, drive train, brakes.

If all that is well, then look for cosmetic issues.

Better to pay a bit more for a pristine car than to buy a cheap beater and try to fix it. I'd say $4K USD is a premium price I'd only pay for a very well maintained and above average example.

Hopefully, one of the other guys will give 87 enhanced advice.

Welcome to the forum.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)