RE: help with fuel for os91vrdf
Gregor,
If you will be using American made synthetic oils, DON'T use purely synthetics.
Your engine will not have much protection and will die young!
If you have access to Sachs Aerosynth II/III, or Aerosave synthetics, you can risk lowering the percentage of castor oil to 2-3%.
If not, use half castor in a 22-23% total oil for this engine.
Even OS don't recommend all synthetics for their ABN engines, like this VR-DF.