I went through the procedure I've used before to replace a bad drive:

 

Stopped the array

Powered down

Replaced drive

Powered the machine on

Here system showed the drive missing, as I expected.  Array was able to be accessed without any missing data while preclear was running.

* Ran Preclear (no errors)

Stopped array and removed bad drive assignment

Restarted array

Stopped array

Assigned replacement drive in proper slot (showed a blue ball)

Start button showed "Start will bring the array on-line and start Data-Rebuild."

Checked the checkbox under it, then clicked start

 

Here's my issue.  Has something changed in the 5.0x series, it starts the array with the drive orange-balled, and says on the left "Data Is Invalid", and never starts the actual rebuild.  There's a 'rebuild parity' button under Stop Array (I haven't clicked it).  What's the next step?  The old drive is still here (haven't sent it of yet), and the array is up with the parity-backed data still available.  Where do I need to go from here?

Guess nobody out there knows, so I went ahead and clicked the rebuild button, and it's doing as intended.  Verbage on the start button after replacing a drive appears to need to be changed, as it says it'll start the rebuild automatically after hitting Start Array..