Sloper, this is the way! I am about to be convinced that olive can be added to castor without any previous "modifying" since the observed small increase in viscosity seems not to justify the work needed. Also double modifying does not affect measured viscosity, but only give a foggy appearance of suspect nature.
I am working on a new way to make lube, using vegetable oils in a way similar to the blending of mineral (and synthetics) ones.
So far fifty/fifty castor- olive seems the right base stock. This should behave as SAE40.... with added lubricity. I hope to publish observed viscosities for it till 150°C . If necessary I will follow the way of a vegetal viscosity improver for modulating the viscosity.
None did try the chainsaw oil TOTAL CHAINBIO? It seems a promising one.

Ugo