1980 Mercedes Benz 300 SD

My brother found this on craigslist and likes it because it is in overall good shape. What are some common failure points on these vehicles that we need to look out for if we go and look at it?

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.