shares missing after drive failure

Thank you for the reply. The firmware versions on the drives are 2xCC32, CC3C and CC4B. I have entered the serial numbers in the above link, and strangely Seagate says all drives have the latest firmware and don't provide a download link for a firmware upgrade. I say all, but in fact the CC4B drive yields an upgrade, however I have a feeling it's the least important, as all the comments I read are about CC32 and CC3C.

I downloaded the upgrade to CC3D. I understand that the available upgrade is for firmware CC3C only, if this was true then there is no upgrade for two of my drives.
What about them? Will Seagate replace them? According to Seatools there is nothing wrong with them.

They say you should back up the disk before flashing the new firmware. How do you back up a drive that is part of a RAID array? Only thing I can think of is a clone.

After flashing the new firmware, does the drive need re-formatting?

Yes, I switched the NAS off before I took the disk out to check it with Seatools, then put it back in, and powered on.

Thanks for your hints. Yes, I will contact netgear in the hope they can assist me.