RAID 5 Set Suddenly NOT VIABLE!

Question

I'm running an early 2008 Mac Pro with an Apple Raid Card with 4 internal, 1TB drives formatted into a single Raid 5 set. The raid card has had numerous issues in recent years, mainly drives that would unexpectedly drop out of the Raid and list as "roaming".  In those past cases, Apple had me shut down the computer, remove the drive sled of the problem drive, wait a few minutes and replace the drive then restart.  On one occasion, the Raid set was back to normal, on other occasions the drive was seen and I would have to assign it as a spare and rebuild the set.  Everything would work fine until the next time.
In the last few days, I discovered the Mac Pro shut down, after I had left it idle for a while with the screen asleep. When I tried to restart, I was greeted with a blank grey screen, no Apple, no anything.  I tried booting from CDs and external Boot Drives with no luck.  This morning I was finally able to boot onto an external drive and discovered my Raid 5 set is now "NOT VIABLE!"
ALL drives are listed "Verified" and "Good." Bays 1 and 2 are "assigned" while Bays 3 and 4 are listed as "Roaming."  The Volume is showing "Degraded" and the Raid Set is listed as "Not Viable."  I have tried shutting down and removing all the drives then reinserting them (in their original slots) and restarting, but nothing changes.
Is there any way I can get these two drives to assign back to the Raid Set WITHOUT losing all my data?  Is there any way to recover all may data?  Am I hosed here and everything is a loss?
Any help will be greatly appreciated.
Thanks in advance.
Brett B.
Here is a screen capture of what Raid Utility reported:

Answer 1

In my experience, Apple RAID  in general (with RAID card or without) does not tolerate a very high error-retry rate from the Drives.
I had a mirrored RAID that repeatedly became Degraded, and decided to take strong action. I made sure I had two Backups, then pulled out the Drives and erased them with Write Zeroes, one pass. One of the drives had more than 10 blocks that needed to be "spared", so Initialization Failed. I ran the procedure multiple times and found that 30 blocks had needed to be spared. If any of these had been marginal in daily use, it could have caused the drive to get (what appears to be) stuck doing dozens to hundreds of retrys, but still not throw an I/O Error that would bring the system to a Halt.
Google did a very large study and concluded that there is a very high probability that drives with multiple errors will end up being replaced within about six months. They attributed this to a cascade of additional errors that often followed the first group detected, leading to the drive being declared unusable.
In my opinion, just reseating the drive (combined with rebuilding, which does re-write the data blocks) may not be strong enough medicine to fix a recurring problem. A drive may repeatedly be doing multiple retrys on some data blocks, or may have Bad Blocks.
I suggest you Zero the troublesome drives (which takes many hours each). If Disk Utility finds more than 10 blocks that need to be spared, or if the drive runs out of available spares, it will report "Initialization Failed!" Consider such a drive not good enough for use in a RAID and replace it with a new one. Or just rebuild your RAID with different (e.g., larger) new drives.