Warning: WD20EADS Unreliable

I've been using 6 WD20EADS drives since August 2010. I did set the IDLE timer and the TLER function. Recently my Readynas Pro froze and started to become periodically unresponsive over the course of months. Very recently The admin panel stopped being responsive and I swapped out the Readynas as it was under warranty. When I got a new Readynas, two drives immediately showed up as bad. Testing reveals they at least have bad sectors. Swapping them out under warranty.

The larger issue here is that I am down for days, have to do diagnostic work, lost the entire array and the whole system has effectively defeated the purpose of this backup device. More concerning is that the Readynas failed, the new one was immediately responsive and the old one did not catch the drive errors. Anyone have a method to pro-actively find bad sectors and imminent drive failure with these drives? I realize that an option is to drop the drives entirely and RE4 drives or equivalent but given the investment I'd like to avoid that course of action at present (I may end up having to go that way in the end for a simple, reliable setup).

Presently, the only thing I have come up with is to do an offline "Test Disks" event at the boot menu on a recurring basis (perhaps monthly on a reminder) but I would prefer a more automated method with notifications.