Linkstation 420 reporting errors and degraded RAID - how to rebuild?

[aenow]

I have a Buffalo LinkStation 420 4 TB model (LS420D0402) configured in RAID 1 mode. It was purchased eight months ago and we haven't had any problems. Two PCs in our office have always connected to it, but when we recently added a Mac to the users list, the drive has had occasional issues connecting, with occasional pop-ups that computers have "lost connection" with the NAS.

Now, the message from the system is:

Error:
E30: Error on drive 2 (2015/09/01 01:00:08)
Status:
I12: The RAID array is in degraded mode. (2015/08/31 11:06:00)
I32: Drive 2 detected. Rebuild the RAID array or format the drive. (2015/08/31 11:06:45)

The main drive is actually still fully functional, and we're able to access files as usual (except for the occasional disconnections which are new). The drive's files are backed up nightly to an online cloud solution.

In the RAID configuration, it reports Drive 1 as "normal" but Drive 2 as "failed" with a size of 0GB.

My questions:

1)  Is it possible to try rebuilding the raid with the existing drive, or is that drive fried by definition?  Is there any way to see if the drive's actually okay without taking it out and running a scan on it?

2)  Is the drive replacement (if needed) covered under warranty?  (It's less than a year old.)

3)  Are these drive/raid errors related to the occasional disconnection problems we've been having since adding the mac user to the mix, or is that just a coincidence?

I sent a message to support yesterday morning but haven't heard back, and thought this might be a faster way of figuring out what I should do next.

Thanks guys!