Barshifter, I agree, Castrol R is a great smell! I also remember it very well from the late 1960s when I first learned to ride a bike, which was a methanol fuelled BSA grass-track racing bike.
I recently used up the last of my main castor oil stock as an additive in my trials car's fuel tank - just for the smell, for old times sake. Many people commented on it, including one younger chap who told me there was something very wrong with my car - because it smelled funny!!
Silkolene certainly used to make a castor based 2T oil but I'm not sure if it is still available. I was given some when I bought my 1970's AJS enduro bike. I'll seek out my spares box for the label; although I think it's probably called something else since Fuchs took over the company.
P.S. Silkolene was previously owned by the Dalton family, as in Timothy Dalton, the actor (James Bond etc). My grandmother was their company secretary for many years and so in the 70s I occasionally scrounged a few "freebies" to try out on my old Beesas. Sad to see the Derbyshire factory has recently been bulldozed flat for a housing development.