I'm not sure how the Marine Corps records were filled then. But Army lower level echelon units were typically filed within the battalion or regimental level files. This may have been how the MC also did this but I could be wrong.
Do you have any information about the unit your searching for.
The units I am searching for records from are:
2nd Marine Battalion, 1st Marine Regiment, 1st Marine Division in Vietnam Dec 1967 thru May 1968.
2nd Marine Battalion, 27th Marine Regiment, 1st Marine Division in Vietnam May thru September 1968.
3rd Marine Battalion, 9th Marine Regiment, 1st Marine Division in Vietnam September 1968 thru January 1969.
I have almost all of the Command Chronologies from each of these however they only contain after action reports by company headquarters staff. I am looking for the day-to-day reports/notes from team, squad, platoon leaders.