for an application API like help, syllabus, gradebook, etc., the proper place to put the API is in:
org.sakaiproject.api.app.XXX
where XXX is the app's package name. These are APIs, and "app" (application) APIs.
Other package roots of interest are
org.sakaiproject.api.kernel.*
org.sakaiproject.api.common.*
org.sakaiproject.api.edu.*
It's not org.sakaiproject.service.*
Don't forget the "app" part.
For example, the gradebook API's manager should be:
org.sakaiproject.api.app.gradebook.GradebookService.
The cover for this should be:
org.sakaiproject.api.app.gradebook.cover.GradebookService
The help manager should be:
org.sakaiproject.api.app.help.HelpManager.
Speaking of "manager", the key guy in the API should be called a "manager" not a "service". So gradebook's API's big player should really be:
org.sakaiproject.api.app.gradebook.GradebookManager.