Old DB machines are out of warranty and should not be used for production services, they need to be effectively put out of service. Also, some needs to be unracked in order to rack the new ones that replace them.
However, before decommission of those old dbs, some of them were old masters, which means they probably hold the most accurate db schema- so we must check there are no data differences with the current masters and any other slaves before deleting its data.
Also, fix the issue with 'mysql' user account not being a system account (uid>999, or whatever is the configuration). It mostly affects these older machines.
These machines are no longer on production, please proceed now