s1 primary master db1052 needs to be decommissioned (T186320) and it is also blocking row B switch upgrade (T183585)
The candidate master is db1067.
This a checklist of what needs to be done before the failover
 Verify db1067 has STATEMENT as binlog format
 Upgrade micro-code and reboot on db1067
 Pick a date for the failover:
 Communicate liaisons to handle the read only time
 Prepare and do the actual failover