I do agree the msdb.sys.syslogins shouldn't be used.

Another way is to use the SUSER_SID function:

SQL 2005 Maintenance Plans

UPDATE

[msdb].[dbo].[sysdtspackages90]

SET

[ownersid] = SUSER_SID('sa')

SQL 2008 Maintenance Plans

UPDATE

[msdb].[dbo].[sysssispackages]

SET

[ownersid] = SUSER_SID('sa')