I believe the manual you are looking for is the Mercedes "Service Manual, Passenger cars Starting 1968 Series 108-109-111-113. Maintenance, Tuning, Unit Replacement".This manual covers these cars manufactured from 1966 to 1973: 280S/8-280SE/8-280SEL/8-280SL/8-300SEL/8 6.3-280SE/9 3.5-300SEL/9 3.5
I have one but it's not for sale. If you want specific information, I will be glad to look it up and send it to you.
Bill Lewallen Lexington,Ky.