The 2008 does have the single row timing chain so if the front's a bit noisy you might want to put aside for a new chain - preferably a stronger one - see yd25.com.au for a great solution (if it's needed).
Hoses are the next problem, particularly the vacuum lines on the turbo actuator. They're not expensive to replace.
If it's a manual it might have a dual mass flywheel which is a pain in the ass for towing. If it's an auto no drama - but the manual needs to have the flywheel, clutch and pressure plate removed and replaced with a single-mass flywheel and HD clutch (Exedy make one that's orright).
Other than that, they're not bad. I would hope the previous owner got sick of the rear suspension dragging its ass around and upgraded the leaf springs already but just check that you can fit your hand sideways above the rear tyre under the guard. Look at my sig - that's a sagged original suspension.
And with all that said - the previous poster's advice about stretching for a new one has a LOT of merit. More powerful engine that uses between 2 and 3 LPHK less fuel - that adds up to a bit of a saving on its own (over 20,000km that's between 400 and 600 litres of diesel). More features inside, and a new car warranty. The new 140kW (now called the D40 ST, because the STX has the V6 diesel) has an electronic turbo actuator and it looks like they've gotten the bugs out of that too, so a new 4-banger isn't a bad deal.
Either way, good luck with the purchase.