I agree with you, Hatterasguy, about Mobil 1 being the way to go. But I'm a little concerned about switching my 11 year old M104 over to a synthetic. I'm nursing a very slight head gasket leak, and I'm worried about the synth potentially clearing out any grit/crap in the seals that might be keeping my head gasket problem at the minor seepage stage. I've seen this happen on plenty of older cars and I don't want to take the chance on mine. Hence my switching of viscosities through the year with the dino oil. If I was running synth, I'd just run 5w40 all year and forget about it.