there is oilcooler on all powerstrokes and it is possible for the o o rings to leak with, but a rebuild kit is like 40 bucks and is easy. The cam position sensor is a sensor located just above the harmonic balancer and the most common problem with these engines, again you can get the part for 30 bucks and a single 10mm bolt holds it in place. Other things include oil leaks at the turbo, few fuel leaks, and injector o rings, all of which are pretty easy to replace.
There are 6 head bolts per cylinder so headgaskets arent a problem. The stock turbo huge so you can make some pretty decent horsepower with it using mild tunes. If you want to go crazy with power there are quite a few modifications that can be done, some a little pricey.
I dont care what anyone else says, check to see if the truck has an oiled air filter in it like a k and n. These tend to let more fine pariculate in and can "dust" the motor. If there is a oiled filter in the truck, check the turbo fins to see if they are eroded away. Also water pumps like to go out on these trucks, but if its got 240k on it, im willing to bet its been replaced and adding a coolant filter will substantially increase its life.
other than that, basic things to check for when buying any car, tranny shifts smooth, leaks, matinence records etc.
I bought a rust free truck last year with 200k on it and use it as a daily driver, thing runs like a champ.
ALSO read this article found in the technical section of the website
good luck any questions arise ask us, we can talk you through just about anything