I'm on my 3rd cutting also. I mow 15 lawns varying from 1.5-3 acres with a ZD331 or ZD326. The 331 gets used the most at 1500 hours, and the 326 was sidelined at 1600h.
My only complaints are starter problems on both, which was rectified with a relay for the starter solenoid, and a fuel supply issue on the 331 that was "fixed" by adding a secondary fuel pump out of desperation. I do have an additional 2 micron fuel filter on both machines which may have pushed the 331 over the edge on fuel delivery with the single OEM lift pump.
All in all, these are nice machines, and a joy to mow with.