Readynas 104: Second Seagate Barracuda to fail

I just wanted to submit a support ticket but apparently Netgear abandoned individual customer support altogether, so this is my only option.

The problem is that, within 3-4 months, a second Seagate Barracuda 3TB HDD has failed without warning. Now, at first the Readynas seemed bricked, but somehow it got back on-line again. Now, the web interface tells me the Readynas is healthy, the volumes are ok but still I can't access files on that drive. 

Problem #1: I can still 'see' the failed HDD and  its contents but trying to copy off the files to another destination results in a network error under Windows (10). How can I rescue these files, either from within the ReadyNAS or externally?

Problem #2: As this is the second HDD failure (the first was immediately total, I had to bin it), how can I avoid failure of the other 'Cudas'? Both failures occured on DLNA access, i.e. playing a video file over the network. Is ReadyDLNA somehow responsible for the failures or could it be incompatibilities with Seagate Barracudas (they are on the hardware compatibility list, however).

All 4 volumes are configured as simple individual volumes, no raid or anything, though they are marked XRAID.

I fervently hope that these disastrous problems can be resolved in this way, as there's no real customer support from Netgear (which, I may add, is disastrous in its own right).

Thanks for any help offered!

Marco