Raid 5 vol wont mount after disk1 swap/disk4 warning

[bmac88]

TS-453A with 4 drives in Raid 5... firmware 4.5.4

I had so many errors on Disk1 that I swapped the drive - not sure if the "new" drive was blank from RMA or pulled out of another drive slot on the same array.
Disk1 is showing "Not Member"; Disk4 has a few SMART errors (below manufacturers threshold) and WARNING
Raid Group status shows "Degraded"

No activity or rebuild status.

Warning notifications show: The default shared folders (Public, Web) are inaccessible. The system volume is locked. You must enter the volume encryption password or upload the encryption key to unlock the volume.... (this NAS isnt Internet facing so i doubt this is an extortion scam)

How can I "join" the new Disk1 to the Raid Group so it can auto-start the rebuild?
Is it possible that Disk1 was part of an old RAID group so it cant rebuild?