Bit new to Mercedes but not new to wrenching. Have an 89 300SE with the M103 engine. I am trying to get my service manuals together but since MBUSA no longer sells the W126 Service CD's I am searching for alternatives. The car did come with the M103 engine manual and the W126 HVAC service manual though. I need the body manual so I can do brakes soon.

I cannot find in the M103 service manual what the proper plug gap is. I just returned from the dealer with 6 Bosch Non Resistor plugs (the box is even marked H9DCO) and they look to be pre-gapped to .8 MM on the box. Is that the correct gap?

Oil - the Previous Owner was running Castrol 10w40 in it. It has 147K on the clock and new valve seals, head gasket and lifters. I have to fix a leak on the upper timing case but other than that no bad leaks. Is 10w40 ok to use in the hot summers here? Temps are in the upper 80's to high 90's during the summer. I was thinking of a partial synthetic oil like Mobil 1 Drive Clean.

I have the gaskets coming for the Timing case leak and at that time I am putting in all new Plugs, Bosch wires, Bosch cap and rotor. The Cam seal as well as the valve cover gasket will be new.

Thanks in advance for the info!