Unless you are prepared to service the lcs, or unless someone has already done it, I'd say don't touch it with a bargepole, because it is likely to fail. Air cooled units are a much safer bet if you want a trouble-free life. The coolant used was corrosive, so leaks are a serious business: inspect carefully before laying out any cash!

On the other hand, servicing a machine that has not leaked (yet) is basically just mechanical, and once serviced, the machine should run fine for another few years.

Somewhere I read that there are issues with large drives, but I have not seen this myself. Realistically, though, a mere 500GB is more than enough for more or less anything you are going to be doing with a G5.