Ok - you have a slightly odd situation, /dev/sdb3 was labelled as failed by the webconfig in your first post, however appears to be functioning as the only partition in array md1. Have you rebooted since your original post? that would explain the drive letter changes
We can try to rejoin your other partition if your certain the drive is still OK?
mdadm --manage /dev/md1 --add /dev/sda3
Then monitor the resync with 'cat /proc/mdstat' and any I/O errors in 'dmesg'