What is the difference between a service manual and a maintenance manual?
I don't see the definition in the FAA site.  But based upon experience in military aviation we look at them as synonymous terms. The terms differ at the frequency and level of care provided by maintenance technicians.
https://www.faa.gov/guidance/
Maintenance manuals are aligned with the term Operations &amp; Maintenance manual, which is for daily operations maintenance and corrective actions.
Service manuals are for longer interval maintenance practices when the aircraft is in the hangar undergoing longer maintenance projects.
Ex:  engine flush vs engine disassembly