Buying John Deere 450J

I'm looking at buying a 450J for logging and wondering what to look for when I'm assessing the machine. It's a 2006 with 2900 hours, and has the extended life undercarriage. What kinds of issues are common for this machine? Is there a way to test the hydrostatic drive motors? Any thoughts or pointers would be helpful.

Buying John Deere 450J