Get a late 2012 model if you can so you won't have the steering lock problem and you will have an oil cooler as well. Generally speaking, the later year models will have less issues. But even if you get a 2009 model it's not end of the world. 370z is a pretty solid car. My 2009 hasn't had any major issues yet. Search the forum for the major problems like steering lock failure or the CSC failure so you will have an idea. Good luck.
Edit: These are the common problems a used(early models) 370z could have. You can start from there.
Question about common problems