The big thing to look out for is rust. Mechanical problems are easier to deal with than rust. If you look at this thread
https://www.volvoforums.org.uk/showthread.php?t=312429 you'll get a good idea of where 240s tend to rust. The thread will also give you a good idea of what it takes to repair it. Estates rust under the tailgate too.
Good luck -- a well sorted 240 estate is a very practical and comfortable not quite classic car.
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Present: 1990 240GL saloon, 1992 240 estate
Past: 1988 240GL; 1971 144DL; 1972 145DL